When Neri Carranza went to see the apartment on West 109th Street in Manhattan, she folded money into the pocket of her blue jacket, just in case she liked the place. This would be the first apartment she had ever looked at, the first time she could make a home of her own, paid for with the earnings from her first job, at a glass factory. And the apartment was exactly as her friend from church had described it: small but comfortable.

So on a freezing Sunday in 1956, Ms. Carranza, then 32, with a crown of black hair and a fierce desire for independence, moved into the narrow two-bedroom apartment. She made it her own, cleaning and decorating every Sunday, planting yellow roses and hot-pink geraniums in window boxes, painting the walls white when they needed a new coat. As landlords came and went, Ms. Carranza stayed, becoming a fixture in the largely Latino neighborhood.

Ms. Carranza in the 1950s. She became a fixture in her neighborhood, staying in her small two-bedroom apartment as landlords came and went. Then the Orbach Group snapped up her building and 21 others nearby. Ángel Franco for The New York Times

“I had everything I ever wanted,” Ms. Carranza said.

But one day in 2010, when she was 87, Ms. Carranza learned that her new landlord wanted to evict her for what seemed like the most nonsensical reason: She supposedly didn’t live in her own beloved home.

She was hardly the only tenant facing eviction by the owners, the Orbach Group, a New Jersey-based company that had recently paid about $76 million for her building and 21 others nearby, a Monopoly move that effectively snapped up most of the residential real estate along a block of West 109th Street. Orbach had filed eviction suits in housing court against scores of her neighbors in rent-regulated apartments.

What happened to Ms. Carranza and the others shows how New York City’s housing court system, created in part to shelter tenants from dangerous conditions, has instead become a tool for landlords to push them out and wrest a most precious civic commodity — affordable housing — out of regulation and into the free market.

Rent-regulated apartments, often the only homes in New York that people of modest means can afford, are vanishing as gentrification surges inexorably through the city’s neighborhoods. Mayor Bill de Blasio, now in his second term, has staked much of his legacy on alleviating this crisis of disappearing affordable housing and rising homelessness.

Yet the city’s efforts to create new affordable housing are locked in a duel with a countervailing force: powerful incentives for landlords to do everything possible to take existing affordable apartments away.

It’s not just that the city’s booming population and economy have spawned a wildly lucrative free market. The entire structure of tenant protections — while probably still the nation’s strongest, at least on paper — has been steadily eroded by landlord-friendly laws adopted in Albany and haphazard regulation.

Landlords, especially the corporate owners who control an increasing share of the market, follow a standard playbook to push tenants out. That is often the first step toward raising the rent enough — beyond $2,733.75 a month, under current rules — to break the shackles of regulation. Owners may offer tenants buyouts to leave. They may harass them with poor services and constant construction. And, sometimes on the flimsiest of evidence, they may sue them in housing court.

(Read about how landlords have exploited weakened laws and fragmented bureaucracy to remake buildings and neighborhoods, in Part 1 of this series.)

It is impossible to say how many evictions are unjust. Many people sued for eviction do owe some back rent, and some tenants certainly abuse the court system, remaining in their apartments for months without paying. For small landlords, such tenants can mean fiscal ruin.

But an investigation by The New York Times illustrates how the Orbach Group and other mega-landlords exploit a broken and overburdened system. In one of the busiest courts in the nation, errors often go uncaught and dubious allegations go unquestioned. Lawsuits are easy to file but onerous to fight. Landlords have lawyers. Tenants usually don’t, despite a new law that aims to provide free counsel to low-income New Yorkers.

Landlords rely on what amounts to an eviction machine. A cadre of lawyers handles tens of thousands of cases a year, making money off volume and sometimes manipulating gaps in enforcement to bring questionable cases. Punishable conduct is rarely punished.

Process servers, required to notify tenants that they are being sued, sometimes violate the law. Among tenants whom servers had supposedly talked to in person, The Times found several who were abroad at the time. One had been dead for years.

Judges sometimes unwittingly ordered the eviction of tenants who had no idea they had been sued.

“When they sent the marshal, they never gave us no notice,” said Zanden Alzanden, a Yemeni immigrant who was evicted from his home in the historic Dunbar Apartments in Harlem when he was in the hospital in January 2017. “Nothing on door, ever. Only that day, the marshal coming in, my son and an old guy sitting in there: ‘Boom boom, get the hell out of here.’”

The Dunbar Apartments, built in the 1920s, began as a grand experiment in housing reform. After buying the Dunbar, E&M Associates began pushing out longtime tenants, remodeling vacant apartments and charging far higher rents. Demetrius Freeman for The New York Times

To see what happens when vulnerable New Yorkers are cast into this eviction bureaucracy, The Times analyzed a database of more than a million housing court cases filed between 2011 and mid-2016. The Times also interviewed hundreds of tenants, lawyers and tenant organizers and examined in detail more than a thousand housing court cases from the past decade. It looked especially closely at two places: the Orbach buildings on 109th Street and the Dunbar Apartments two miles uptown.

What emerged were often-overlapping modes of harassment: by landlords’ fraudulent or exaggerated claims, by disrepair and by overall court dysfunction.

About 232,000 cases were filed last year against tenants, roughly one for every 10 city rentals. Most tenants were accused of owing back rent. But in many cases, tenants were sued for rent they did not owe. Sometimes they had paid, only to have landlords claim that the checks mistakenly remained uncashed or had been lost in the mail; sometimes they were sued for money owed by a government program. Sometimes, tenants withheld rent only because much-needed repairs had never been done.

In recent years, landlords have also increasingly turned to a different kind of eviction suit, like the one against Ms. Carranza. Known as holdovers, these cases involve purported lease violations. Often the violations are minuscule. Sometimes they are simply fabricated. Even as the overall number of eviction lawsuits has fallen over the last decade, the proportion of holdovers has grown, particularly in Brooklyn and Queens, epicenters of gentrification. A decade ago in Queens, about one in six lawsuits was a holdover. Last year, roughly one in four was.

Even if a case is shown to be baseless, just being sued can hurt a tenant’s ability to rent a new apartment. Screening companies tell landlords whether a prospective tenant has been sued for eviction, without necessarily saying how the case was resolved. Attempts to abolish this “tenant blacklist” have so far failed.

The dislocations from housing court can echo for years. Although evictions are relatively rare — there were about 21,100 last year — many tenants, tired of battling, decide to leave on their own. Some end up doubled up with relatives or in homeless shelters. At the Dunbar, more than a quarter of the tenants sued since 2013 have left.

Fallou Diop, whose family lived a few doors down from Ms. Carranza on 109th Street, was sued twice by Orbach: in 2009 for falling behind on his $1,144-a-month rent, and in 2011 for allegedly subletting rooms in his apartment. He paid his back rent. The “subletters” were relatives who had lived with him for 19 years. But about two years after winning the second case, Mr. Diop agreed to leave.

“I was sick of fighting with them and sick of the harassment,” said Mr. Diop, a retired baker who said he took a $50,000 buyout, a seeming fortune at the time. He then rented an apartment in the Bronx for $2,700 a month.

In June 2016, Orbach advertised Mr. Diop’s old apartment, urging prospective tenants, in capital letters, to “call today to view this beauty.” The monthly rent would be $4,200.

The deal did not work out so well for Mr. Diop. The buyout money ran out. At 65, he sleeps on his ex-girlfriend’s couch.

A Court System Hijacked

With a monthly rent of about $300, Ms. Carranza’s apartment was a prime target.

Ms. Carranza’s apartment was crowded with furniture, but well kept. Her landlord, the Orbach Group, sued her for eviction in 2010, claiming that the unit was so filled with trash as to be “uninhabitable.”

In July 2010, the Orbach Group filed its holdover suit against Ms. Carranza, charging that she was illegally using her apartment as a storage unit while living with a nearby friend. Court documents called the apartment “inaccessible and uninhabitable,” packed with newspapers and trash.

Photos taken five months earlier by Ms. Carranza’s niece showed her sitting in the apartment, watching TV. It was crowded with furniture but well kept, with no newspapers, no trash.

Ms. Carranza’s apartment suffered water damage, along with moldy walls, rusted fixtures, broken flooring and sagging ceilings.

But mold covered the walls. Light fixtures and kitchen cabinets had rusted out. Parts of the floor had come up. The kitchen ceiling sagged.

Housing court was not supposed to be used this way, as a cudgel against tenants in decrepit housing. The system was created in 1973 with a very different mission: to foster the repair and preservation of New York’s aging housing stock. It also aimed to provide a single forum for landlord-tenant disputes, which had overwhelmed civil courts.

Repairs were ordered on Ms. Carranza’s apartment but were never done.

Within a few years, it was in trouble. A scathing 1979 city comptroller’s audit said the courts had failed to crack down on bad landlords. In 1986, a task force of tenant advocates and lawyers described a system in chaos. Their report quoted one judge saying, “I don’t have time to breathe, I go from one case to another.”

(Go inside Brooklyn’s housing court, last stop on the road to eviction, in Part 3.)

The court soon crashed headlong into a business opportunity.

After years of suburban flight, urban malaise and fiscal crisis, New York in the early 1990s was a city on the rebound. Neighborhoods previously considered off-limits to the upwardly mobile began to gentrify.

At the same time, state lawmakers gutted protections for tenants in rent-regulated apartments. Large companies scooped up buildings, trying to flip affordable apartments into luxury rentals or convert them to co-ops or condominiums.

A company called the Pinnacle Group helped turn housing court into a weapon. In 2004, Pinnacle started buying hundreds of buildings around the city, often with partners. In August 2005 alone, Pinnacle and Praedium Group, a private-equity firm, bought 104 buildings, including Ms. Carranza’s building and the Dunbar. By 2006, Pinnacle had filed about 5,000 eviction lawsuits, almost one for every four apartments.

Pinnacle was so large and aggressive that it ran into problems, including an attorney general’s investigation and a tenant class action, both of which settled. Prompted in part by Pinnacle’s tactics, the City Council passed a law in 2008 letting tenants sue for harassment, although it would prove largely ineffective.

Around the same time, Pinnacle advertised its 22 buildings on 109th Street. It wanted a single buyer.

The Orbach Group was a relatively new player in New York. Meyer Orbach, who grew up in his family’s real estate business, had formed the company about six years earlier, focusing on commercial and high-end residential properties. But as the 2008 financial crisis hit, the Orbach Group entered the regulated game, buying 13 buildings on West 49th Street. In May 2009, Orbach bought Pinnacle’s buildings on West 109th.

Meyer Orbach’s company, the Orbach Group, began buying up buildings with rent-regulated units in the late 2000s, around the time of the financial crisis.

Orbach also adopted Pinnacle’s business model. Between 2008 and 2010, it sued 182 tenants, targeting roughly one in three apartments, court records show. Orbach also relied heavily on holdover lawsuits. One in three Orbach eviction cases was a holdover, compared with one in 10 citywide.

Holdover lawsuits have a distinct advantage for aggressive landlords: They can be filed with little proof, yet they can require tenants to go to court repeatedly and turn over years of personal information.

“They are fishing expeditions,” said Michael Grinthal, a supervising lawyer with the Community Development Project at the Urban Justice Center.

Bringing a holdover case requires so little evidence, Mr. Grinthal said, that one Brooklyn landlord filed 23 identical lawsuits, accusing tenants of “smoking and/or drinking and/or gambling and/or loitering.” Shaken, some tenants moved, Mr. Grinthal said.

In response to questions about its use of housing court, an Orbach spokeswoman, Sandra Kittel, said the company was “deeply committed to affordable housing” and had kept thousands of apartments affordable.

To prove that Ms. Carranza was living with a friend, Harry Tawil, the manager of most Orbach buildings in New York, said “a database search” revealed that she had not used her address to apply for credit in almost five years. He also swore that “Neri Carranza admits that she does not reside in the subject premises.”

Ms. Carranza and her friend said this was not true.

Lawyers for Orbach asked Ms. Carranza for documents stretching back almost five years, including hospital bills, bank statements, electric bills, W-2 and 1099 forms, and tax returns. Also any wills and codicils, passport, driver’s license, social security card and birth certificate.

Ms. Carranza, who speaks only Spanish, considered every court document, written in English and slipped under her door, an insult. She was lucky enough to get a lawyer working pro bono, and ultimately she won. But the case stretched for more than three years. In the meantime, repairs were ordered but not done. Punitive damages were sought but not awarded. Still, the papers kept arriving. Ms. Carranza kept going to court.

“When I’d see those papers on the floor, I would say to myself, ‘Those sons of their mothers!’” said Ms. Carranza, who holds a black belt in karate and prefers Lancôme perfume to all others. “I would shake from the anger,” she added. “It was an injustice.”

‘Throwing a Spitball’

The Dunbar Apartments began as one of America’s grandest experiments in housing reform. Built by John D. Rockefeller Jr. in the 1920s and named for the black poet Paul Laurence Dunbar, the complex was the nation’s first large housing cooperative for African-Americans.

One of the center courtyard intersections that connect the Dunbar’s six buildings. The churn and renovations have left the Dunbar in turmoil, divided between old tenants and new. Demetrius Freeman for The New York Times

With six brick buildings overlooking a central garden, the Dunbar is a microcosm of Harlem history in a single city block, at the corner of 149th Street and Frederick Douglass Boulevard. In its early days, the Dunbar was home to the likes of the civil rights leader and sociologist W. E. B. Du Bois and the entertainer Bill (Bojangles) Robinson. It is a city landmark, on the National Register of Historic Places.

Eventually, though, the co-ops became rentals, and the Dunbar slid through a series of owners and stages of disrepair. The current landlord is a limited liability company formed by a Brooklyn company, E&M Associates, which bought the complex in 2013 after a foreclosure on Pinnacle’s mortgage. And with Harlem a real estate hot zone, E&M has worked to remake the Dunbar, pushing out longtime tenants, remodeling vacant apartments and charging far higher rents.

The churn and renovation have left the Dunbar in turmoil, divided between old tenants and new, and sometimes between black and white. To some longtime residents, the fresh paint and gleaming appliances installed next door signify that the landlord is letting their own homes decay to drive them out.

“I’m gonna put it to you straight: They want the black folks to move out,” said Lynette Williams, 80, who has lived in the Dunbar for 21 years. “Because the white people can come in and pay more.”

Through a web of limited liability companies, E&M has an ownership interest in at least 90 New York buildings with regulated apartments, property records show. Until recently, a section of its website aimed at investors boasted that E&M approached every property “from an investor’s point of view, seeking to understand the underlying intrinsic value of the property, as well as the steps that must be taken to unlock that value.” A link to the section for residents was broken.

(After The Times reached out to the company, it took down its website. In response to questions, E&M also said it had “had no involvement with Dunbar Apartments” since mid-2017, although property records show no sale. The company did not respond to requests for an explanation.)

Housing court has helped E&M unlock value. In less than five years of ownership, records show, the landlord has sued at least 250 rent-regulated tenants — almost half the Dunbar — some multiple times. There have been more than 500 lawsuits in all.

Housing court records show only six successful evictions. But 15 more tenants may have been evicted: Records show that eviction warrants were issued, and those people are no longer in their apartments. Eleven other tenants agreed to leave to settle their cases.

But that tells only part of the story: Dozens of others left after being sued. Many said they were tired of going to housing court to fight over repairs. All told, 67 of the tenants who were sued — more than one in four — are no longer living in the Dunbar.

Most Dunbar cases examined by The Times were brought over back rent, as are most eviction suits citywide. And many tenants did owe money.

But roughly a third of the cases either were discontinued because the rent had been paid or were simply dropped, indicating that the case had been filed by mistake, or that the tenant had paid after being sued or had simply moved. That raises questions about whether such suits are aimed at harassing tenants.

In another third of cases, tenants admitted that they had stopped paying rent but also said their apartments needed repairs. By law, tenants may withhold rent to secure repairs.

Several tenants said the only way to get problems fixed was to stop paying rent, be sued and then tell a judge.

“When they took me to court I was frustrated and upset, so I was withholding my money,” said Katrina Stanley, 51, who lives in the apartment her great-grandmother moved into in the 1920s. “They sent an unlicensed person to fix my ceiling. And just as quick as he fixed it, the ceiling fell again.”

Many tenants complained of leaks. One apartment needed so much work, it failed an inspection for federal rent subsidies. One woman was awarded a major rent reduction after complaining of mold, cockroaches and the improper disposal of a corpse in a nearby apartment.

Idrissa Sidibe, 54, a truck driver, moved into the Dunbar in 2001. Over the years, he said, he complained repeatedly about a loose hot-water tap in his bathtub.

Last July, the Dunbar sued Mr. Sidibe for almost $2,600 in back rent, which Mr. Sidibe disputed. Three days before the first court hearing, Mr. Sidibe tried to add hot water to a lukewarm bath when the running water blasted scalding hot. Shocked by the pain, Mr. Sidibe struggled out of the tub, then collapsed onto the floor.

When a judge approved Idrissa Sidibe’s eviction from the Dunbar, he was in the hospital for severe burns from a faulty hot-water tap in his bathtub. Demetrius Freeman for The New York Times

His closest friend found him and called an ambulance. Photographs showed layers of skin peeling off his right foot and burns on his legs. Mr. Sidibe required skin grafts and spent more than seven weeks at Harlem Hospital Center. While he was there, his kidneys nearly failed — and the judge approved his eviction.

“I was in the hospital thinking, ‘How am I going to get out of here and make a payment?’” said Mr. Sidibe, who staved off eviction and sued the landlord for his injuries. That case is pending.

In response to questions, E&M said through its lawyers that because of neglect by previous owners, the Dunbar required vast work to meet the company’s safety, cleanliness and security standards. The lawyers said they could not comment on individual cases but questioned whether tenants had actually left over the lack of repairs or fatigue at going to housing court.

“We believe it reasonable to assume they left without paying rent that was owed and/or to avoid eviction,” wrote Renee Digrugilliers, a lawyer with the firm Horing Welikson & Rosen.

Ms. Digrugilliers said many tenants filed “bogus repair claims” and often made it difficult to do repairs by refusing to allow workers into their apartments. The owner, she said, sued only tenants who did not pay rent or otherwise broke the rules.

Even when cases are quickly abandoned — as in a fifth of eviction suits citywide — there can be significant repercussions.

Laurie Weisman says she was not behind in her rent when she was sued by the Dunbar in March 2017. So she was shocked when a reporter informed her of the lawsuit. (Ms. Digrugilliers said her firm had been given ledgers showing Ms. Weisman behind in rent.)

Laurie Weisman, a Dunbar tenant, was sued twice last year by the landlord. Although the suits were dropped, she is still feeling the effects: The tenant blacklist is getting in the way as she looks for a new home. Demetrius Freeman for The New York Times

“It’s almost as if they’re throwing a spitball and seeing if it sticks,” Ms. Weisman said.

Though that case and another filed nine months later were dropped, Ms. Weisman hopes to move soon. But the tenant blacklist makes finding a new apartment difficult.

“I feel cornered,” Ms. Weisman said. “I don’t want to stay here, but I can’t leave.”

Lawsuit Mills

On April 11, 2017, the law firm Green & Cohen sued three rent-regulated tenants in a building on West 111th Street.

One case was filed and dropped. The tenants in another hired a lawyer, who got Green & Cohen to agree that the lawsuit had been filed in error.

In the third case, the tenant, Carolyn Opalisky, a retired jazz club owner, didn’t hire a lawyer. She signed an agreement known as a stipulation, affirming that she owed about $1,325. The next day, Green & Cohen filed eviction papers, though her first payment wasn’t due for more than a month.

“I did comply!!” Ms. Opalisky wrote in a court response. “So why eviction???”

The judge sided with Ms. Opalisky.

Because few lawyers are ever sanctioned, the system creates an incentive to file as many cases as possible, regardless of merit.

Volume is central to the business model of many law firms that represent landlords in New York. One firm, Gutman, Mintz, Baker & Sonnenfeldt, brought almost 110,000 eviction cases over five years, more than 10 percent of all cases for privately owned buildings.

Some firms, The Times found, repeatedly sued tenants even after being told that they owed no rent. Sometimes rent ledgers were wrong. Sometimes lawyers sued for money owed by government programs, usually not allowed.

Firms often file cookie-cutter suits, filling in rent numbers and landlord names on documents that otherwise remain the same, without verifying landlords’ information. The filings echo abuses committed during the foreclosure crisis, when banks churned through hundreds of documents without reviewing them for accuracy.

And with the barrier to filing a housing court case so low — a $45 fee — the volume is such that each of the 50 judges hears as many as 90 cases every morning, making it easy for errors and even outright lies to slip through. In January, a commission of lawyers and judges issued a highly critical report on housing court, calling the number of judges “grossly inadequate” and saying that at least 10 more were “not simply requested, but mandated.”

Most tenants do not have lawyers, even as big landlords keep lawyers on retainer. At the Dunbar, tenants had lawyers in fewer than 10 percent of the cases reviewed by The Times. Landlord lawyers go from courtroom to courtroom, pulling tenants into hallways to agree to stipulations before they ever see a judge. Tenants who do not speak English face particular problems: In Queens, more than 160 languages are spoken, but the court has staff interpreters for just three, the commission reported. Some tenants said they felt pressured to agree to deals they did not understand.

“They go in there with their fancy lawyers, and don’t let tenants speak,” said Pandora Holt, who has lived at the Dunbar for 22 years and has been sued four times by E&M.

Although a new law aims to provide free lawyers to poor tenants within five years, advocates worry that the city funding for the project is insufficient, and that a heavier caseload could stretch pro bono lawyers and judges too thin.

Judges are hard-pressed to tell if certain landlords are filing inordinate numbers of eviction suits. Housing cases, unlike those brought in other courts, are not available digitally, and often lawsuits identify only the limited liability company listed as landlord, not the underlying owner. Judges can’t even get a full picture of what is happening in one building. On Feb. 5, Horing, Welikson & Rosen sued 38 tenants at the Dunbar. Those cases — among 60 suits that a single lawyer filed that day against tenants in 18 buildings — were parceled out to at least six judges.

Ms. Digrugilliers said Horing, Welikson & Rosen, which also represented Pinnacle when it was investigated by the attorney general, was “as cautious as possible” in bringing lawsuits, and that neither the firm nor its clients intentionally filed meritless lawsuits.

Green & Cohen is considerably smaller than other firms but has represented large landlords like E&M and Orbach. (Orbach appears to have recently stopped using the firm.)

An analysis of hundreds of Green & Cohen’s cases revealed sloppy paperwork in many. The firm sued tenants for money due from government agencies, misstated rents and misspelled names. It submitted erroneous rent ledgers and documents that belonged in different cases.

In 2015, a federal class-action lawsuit against Green & Cohen said that the firm had seemingly used “the same template for all the hundreds of cases that they filed against tenants within the State of New York within the past year,” and that it had determined that meaningfully reviewing cases before filing was “not as lucrative as the filing of pleadings and motions” without review. The case was confidentially settled.

Green & Cohen did not respond to repeated requests for comment.

Even lawyers who engage in misconduct are unlikely to face penalties. Between 2011 and 2016, landlords or their lawyers were sanctioned or cited for contempt in housing court fewer than 50 times. The court doesn’t even track lawyers or landlords who get in trouble.

Housing court judges rarely impose sanctions unless lawyers request them. But more than two dozen tenant lawyers said they feared seeking sanctions.

In October 2016, for instance, Orbach sued Margarita Galvez, saying she owed more than $12,000 on her Upper West Side apartment. Green & Cohen pursued that lawsuit even though Ms. Galvez’s lawyer, Rachel Hannaford, insisted that the rent had been paid. The rent ledger itself showed a $138.50 credit.

Ms. Hannaford asked for sanctions, but only against Orbach. “I knew that my little lawsuit wasn’t going to get Green & Cohen sanctioned, and didn’t think it was worth the risk and the harm to future clients,” she said.

Ultimately, as part of a stipulation, she dropped that request. Ms. Galvez had not wanted to drag out the case.

Ms. Carranza also ran afoul of Green & Cohen. In July 2014, almost a year after the last court date in her first case, Orbach sued her again, saying she owed about $5,500, more than half her annual income.

“The neighbors would tell me, ‘The landlord is saying you owe a lot of money,’” Ms. Carranza recalled. “Can you imagine? I was so embarrassed.”

It took her lawyers almost seven months to prove that whatever rent was missing was owed by a city program.

Poorly Served

Wesley Moise is a process server, charged with notifying tenants that they face possible eviction. Judging from entries in court records, he also appears to have acquired some of the salient skills of a mountain goat.

On March 24, 2017, Mr. Moise reported, he delivered notices to six Dunbar tenants in 12 minutes.

The Dunbar has 44 stairwells and 536 apartments. Each stairwell has its own front door. There are no elevators.

Yet Mr. Moise claimed that, in those 12 minutes, he raced from the third floor of one stairwell to the fourth floor of another stairwell, to the sixth floor of a third stairwell, to the third floor of a fourth stairwell, to the third floor of a fifth stairwell and finally back to the fifth floor of the fourth stairwell. Each time, he needed to ring a doorbell and be let inside the building.

“I know this building,” said Julio Almonte, who lives in the fourth apartment Mr. Moise claimed to have visited that morning. “Even if I wanted to, there’s no way I could go to six different apartments in 12 minutes.” Mr. Moise, he insisted, did not show up at his door.

A process server’s job may sound mundane, but it is crucial: A tenant who does not appear in court can end up evicted after a default judgment. “You have to get notice and be able to defend yourself,” explained housing court’s supervising judge, Jean T. Schneider.

The Times examined hundreds of cases involving an agency that contracts with Mr. Moise, Howard Belfer Inc., which is routinely hired by law firms representing Orbach and E&M. A range of problems emerged: improbable routes, hard-to-recreate travel times, signatures by one notary public on top of another’s typed name, and in-person encounters that tenants say never happened.

In an eviction case, a landlord must try to notify a tenant in person on two separate occasions, with two separate documents. Each time, a process server should knock and wait several minutes, returning another day if no one answers, according to case law. If there is still no response, the server must leave a notice on or under the door.

There is one further opportunity to alert a tenant in person. The landlord is supposed to verify that the tenant is not in the military or dependent on a service member, a federal requirement protecting military families from eviction.

But the courts depend on process servers and those who file nonmilitary affidavits to do what they say. Servers must keep GPS tracking data, which is notoriously fuzzy, and log books, but audits are rare.

About 33,000 tenants last year faced judgments for failing to appear in court. It’s not clear how often bad service leads to such default judgments. But tenants who first learn about a case from subsequent eviction notices look like scofflaws in court.

Mr. Alzanden, the Dunbar tenant evicted while hospitalized, had to pay more than $4,200 to recover his apartment — for rent he said he didn’t owe, as well as marshal and legal fees and storage of his belongings. “We had no choice,” he said.

A judge can order a hearing when service is disputed; about 800 are held every year. Service agencies are supposed to report them to the city’s Department of Consumer Affairs. Not all comply.

Most violations result in modest fines and consent orders. Instead of revoking licenses, the city usually opts to deny license renewals.

Since 2014, only one agency, JDG Investigations, and five servers have been denied for enforcement reasons. Regulators claimed that JDG, based in Queens, had hired unlicensed people to serve court papers at least 1,800 times.

Others have kept their licenses despite numerous violations. In August 2016, Nationwide Court Services, based on Long Island, settled 287 violations.

Mr. Belfer, who runs the agency bearing his name, has been in and out of trouble for almost as long as he has been licensed. In 1987, a civil court judge found that affidavits from Mr. Belfer and another server “are suspect and are not to be granted simple credence.”

In 2012, his agency’s license was suspended for a month. In 2013 Mr. Belfer paid a $60,000 fine and agreed to monitor servers.

Yet his servers continued to have problems. Camera footage showed that one Belfer contractor, Dwayne Thomas, had not appeared when he claimed to have served a legal notice in May 2015, a federal lawsuit says. In 2016, the city denied a license renewal to another server, Hakeem Jamal, in part because he claimed to have served a woman at Vincent Yeats’s apartment in the Dunbar one minute before serving someone 17 miles away in Queens.

“It was total malarkey,” said Mr. Yeats, who lived alone and found out about the case days before a possible eviction. “I had such hassle from them, I just gave up and moved.”

Mr. Jamal, who also worked for Nationwide, said it had fabricated the service in Queens. Nationwide disputed that, saying it had been “duped by an unscrupulous server.”

Mr. Thomas and Mr. Moise did not respond to requests for comment.

Ms. Digrugilliers, the lawyer for E&M, said Mr. Belfer’s company was one of several used by her firm. She said the firm was not aware of any fine against Mr. Belfer’s company, and disputed tenants’ claims of being improperly served.

Last fall, The Times requested public records on Mr. Belfer’s company from the Department of Consumer Affairs. In late February, after months of extensions to gather documents, the agency denied much of the request, citing an investigation into Mr. Belfer.

At the Dunbar, Mr. Belfer handled many of the nonmilitary affidavits himself. He reported speaking with 15 tenants in 2016 and 2017, one twice.

But all 15 tenants told The Times they had never met Mr. Belfer. Two were out of the country when he said he visited them. Five had moved out.

Mr. Belfer also claimed to have spoken to another tenant, Edward Robinson, on Dec. 5, 2015. Mr. Robinson had died — 22 years earlier.

There was significant fallout: Since 2015, six tenants whom Mr. Belfer claimed to have spoken to were locked out. Three had to pay legal and marshal fees to recover their apartments.

When a reporter visited his Long Island office, Mr. Belfer said he did not want to discuss his business. But when asked about nonmilitary affidavits at the Dunbar, he responded: “These people do not pay their rent. They will say anything to anybody.”

A Neighborhood Changed

The Orbach Group’s buildings on 109th Street illustrate how a landlord can alter a neighborhood. Once an apartment empties out, workers chop it into smaller rooms and install new fixtures, all catering to students at nearby Columbia University.

Orbach even markets the neighborhood as “CoSo,” for Columbia South, and has advertised on the university’s internal housing site.

College students don’t complain much, don’t know much about rent regulation and don’t stay long. Every new tenant means an opportunity for a higher regulated rent, until the apartment hits the free market.

The plan is working. In 2009, when Orbach arrived on 109th Street, 285 of the 381 apartments were rent-stabilized, the most common kind of regulation, tax bills show. But by 2016, the most recent data available, only 121 were.

Orbach’s aggressive use of housing court attracted the attention of the state attorney general’s office, which in 2015 informed tenants that Orbach was under investigation, in part for “frivolous eviction proceedings.” By then, Orbach was filing far fewer lawsuits, though it still relied extensively on holdovers. That investigation continues.

Orbach now owns about 75 buildings near Columbia. Meyer Orbach has branched out, buying into the Minnesota Timberwolves N.B.A. team and guiding his company into a new market: buildings that depend on federal subsidies for the poor.

In November 2014, at age 91, Ms. Carranza was living on about $830 a month in what her lawyers described as “horrendous conditions.” She had been through 19 court dates.

That month, a judge ordered Orbach to fix the apartment. Because the work would be so extensive, Ms. Carranza’s belongings were moved into storage. She went to stay with her niece, Melinda Torres in Carlisle, Pa. The family regularly visited the empty apartment to check on repairs. Nothing much was done.

By June 2015, the apartment had no running water and was infested with roaches. Ms. Carranza sued the Orbach subsidiary that owned her building in housing court to force repairs. Separately, she sued the Orbach subsidiary; Mr. Tawil, the building manager; and Green & Cohen in federal court for violating the law prohibiting unfair or abusive debt-collection practices.

But by spring 2016, tired and worn down, her apartment still in disrepair, Ms. Carranza decided to settle, for about $100,000.

Ms. Kittel of the Orbach Group said Ms. Carranza had consistently demanded a six-figure payment to relinquish her apartment, despite the fact that she was living in Pennsylvania. “We believe that Ms. Carranza truly demonstrates how broken the system is,” she said.

Ms. Carranza now lives with her niece in Pennsylvania. “I lost everything,” she said. Ángel Franco for The New York Times

Ms. Carranza now lives with the Torreses, near cornfields, barns and woods. There is no church with services in Spanish. No grocery catering to Latinos. No old friends to visit. There are not even any sidewalks.

She spends her days inside, mostly alone. She cooks for herself on a hot plate, fried chicken legs and potatoes.

“I lost everything,” she said. “I feel so bitter inside, and I don’t like it.”

Every month or so, her relatives drive her back to New York, back to her neighborhood. It is always bittersweet. A yoga studio has replaced her karate school. Where a 99-cent store once stood, Orbach has set up a real estate office: “CoSo,” a sign announces in big blue letters.

Last fall, Ms. Carranza returned to close her bank account. She stood in front of her building, surrounded by friends, telling them that there were no Latinos in all of Pennsylvania.

“There’s no one to talk to,” she said. “You can talk to the trees.”

Ms. Carranza’s name was still on the buzzer at her old building on West 109th Street when she visited last fall. Ángel Franco for The New York Times

Her name was still on the buzzer at 247 West 109th Street. After a tenant invited her inside, Ms. Carranza ran her hand along the hallway as she walked, pointing out her apartment — No. 2 — and her mailbox.

After years of failed requests for the most basic repairs, her apartment had been completely remodeled — illegally, as no building permit was ever filed, buildings department records show. Two Columbia students paid about $3,500 a month to live there.

Ms. Carranza walked through the home she could no longer recognize, running her hand along the new kitchen counter, touching the new sink, remembering where she used to keep her French dining set, where she used to sleep. A stairway had been added, leading to new basement rooms. She gave one tenant a sideways glance.

“Do you think he’ll leave?” Ms. Carranza asked her niece. She paused, thinking. “What if they’d give me my apartment back?”

She would sit on the stoop again, and she would invite people over for dinner again, and she would fry chicken again. What happiness she would have, she said, if only she again had her home.