Some midsize banks got a massive inflow of deposits during the pandemic and they didn't know what to do with the money, so they parked it in "safe" investments

Some midsize banks got a massive inflow of deposits during the pandemic and they didn't know what to do with the money, so they parked it in "safe" investments like mortgage backed securities. Then when the pandemic subsided, people started burning down their savings accounts, and interest rates started skyrocketing. All the banks' money was tied up in all these 30-year mortgages that nobody wants anymore because they're paying like 2.5% and inflation is 8% now, but they're still forced to sell them for terrible prices just to keep their ATMs full. Eventually word gets out about what's happening, there's a bank run, and the bank starts death spiraling. Massive banks have nothing to worry about because if the government allows them to fail they'll take the entire economy down with them. And (presumably) smaller banks weren't under the same pressure from investors to generate returns on idle capital, so they didn't commit the same sins as the midsize banks.