A few years ago, when our startup was just beginning, our bank simply closed our account out of the blue. I guess it wasn't worth it to them, as we had no revenue yet and bootstrapping, so very little money parked. It took several days to get our money out, we couldn't make payroll and pay vendors in the meantime.

We later opened two accounts in two different banks as a backup/failover strategy. One handled incoming invoices and accounts payable, while the other handled payroll, so we'd always have money flowing through both banks at all times. If one of them failed, locked us out etc. we'd have the other to fall back on. It actually happened once: due to an admin error one of the accounts was locked for 10 days. We just routed payments and receivables to the other bank and went on with our day.