As the one-year anniversary approaches of a crisis that brought down several midsize banks, trouble at another lender is putting unwelcome attention on the industry again.

Concerns now center on New York Community Bancorp, which operates roughly 400 branches nationwide under brands such as Flagstar Bank and Ohio Savings Bank. The bank ballooned in size over the past year, to more than $100 billion in assets, after taking over the fallen Signature Bank last spring in an auction organized by federal regulators.

New York Community Bancorp’s stock nose-dived after it released an ugly earnings report that included unexpected losses on real estate loans tied to both office and apartment buildings. Its shares have lost more than half their value over the past week.

Shares of other lenders with portfolios of commercial real estate have dropped, too, a reminder that what afflicts one lender can affect others, as when fears about concentrated customer bases and low-rate bond portfolios took down a group of lenders last spring. Here’s what you need to know.

What is behind the latest banking worries?

The principal shock in New York Community Bancorp’s earnings report last week came from its admission that the value of its real estate loans had dropped steeply, which spurred it to slash its dividend and sock away half a billion dollars to protect against future losses. The bank identified a pair of loans — one related to an office complex and another for a co-op residential building — that were responsible for as much as $185 million in losses.

Bank representatives, who did not respond to requests for comment, fueled further angst by deflecting analysts’ questions about their expectations for future profits. The bank’s stock plummeted nearly 40 percent after the earnings report and have continued to lose ground, dropping 11 percent on Monday and more than 20 percent on Tuesday.

Moody’s downgraded the bank’s credit rating late on Tuesday, citing “multifaceted financial, risk-management and governance challenges” facing the lender.

A large swath of other lenders, including community banks and private lenders, could also face losses linked to commercial real estate loans, many of which were made before the post-pandemic move to hybrid work put pressure on office landlords and caused the value of their buildings to drop. The rise in interest rates over the past few years has also made it more expensive to refinance such loans.

Which other banks are in the spotlight?

M&T Bank is similar in size and has comparable exposure to commercial real estate, according to Wolfe Research. In its latest earnings report, the bank reported a rise in troubled real estate loans, but analysts said the exposure was “manageable.”

The average regional bank stock has lost 10 percent over the past week.

What about larger banks?

The biggest banks in the United States, such as JPMorgan Chase and Citigroup, have for months been setting aside money to gird for potential real estate losses. They are generally considered better able to withstand a downturn because of their diversified base of lending and depositors. Share prices for the largest banks have recently held up better than those for smaller lenders, and Chase said on Tuesday that it would open an additional 500 branches in the next three years.

What do regulators say?

Jerome H. Powell, the chair of the Federal Reserve, said during a “60 Minutes” interview that aired Sunday that he viewed a real estate-led banking crisis as unlikely. He said that some smaller and regional banks were “challenged,” but that the U.S. central bank was working with them.

Mr. Powell described the situation as a “sizable problem” that the Fed had been aware of for “a long time.”

In testimony on Tuesday for the House Financial Services Committee, Janet Yellen, the Treasury secretary, said she was monitoring current banking stresses but declined to weigh in specifically on New York Community Bancorp. “I don’t want to get ahead of where we should be, given what’s happening,” she said.

Is there any risk of a bank run?

The banking crisis last spring was exacerbated by worried customers who rushed to withdraw their money at once, forcing several banks to halt withdrawals as they rushed to raise cash. (Banks are required to keep only a fraction of customer deposits on hand.) Thanks to the widespread usage of mobile banking and electronic transfers, such a phenomenon can now happen quicker than ever.

There’s little indication that New York Community Bancorp is near that precipice. The bank’s executives said last week that deposits had fallen only 2 percent in the fourth quarter.On Tuesday, the bank issued an update on its finances, noting that deposits had risen since the start of the year, to roughly where they were before the decline in the fourth quarter.

Thomas R. Cangemi, New York Community Bancorp’s chief executive, said in a statement that the bank was investing in “a risk management framework commensurate with the size and complexity of our bank” The Moody’s downgrade would not have a “material impact” on the bank, he added.

Are there any immediate reasons for bank customers to worry?

A falling stock price does not directly impede a bank’s day-to-day operations. New York Community Bancorp’s branches continue to operate normally, and each customer is protected by government insurance of $250,000.

Even for accounts above that level, regulators usually organize auctions in the event of a catastrophe (as they did last spring) in which failed banks are taken over by healthier ones, with an aim of protecting ordinary account holders.

Alan Rappeport contributed reporting.