I didn't provide details of the transaction because I was more interested in what to do next and not have people speculate on the reason.

The transactions in the account are rental payments from a tenant and bills paid related to the rental. The account has had the same types of transactions for 4-5 years. It is a shared account with someone else (because I only own part of the rental), so it's possible I am being caught up in something related to them. They are closing that shared account and my personal accounts.