Is there an expiration date on bans for AML/high risk customer reasons? I have had bank account closures dating back to 2015. I am wondering if some day I will be able to use these banks again.

it depends on the bank and the reason for the account closure. If the bank chooses not to bank with high risk customers then you're better off looking for someone that will.

There is no formal expiration date for an account closure due to a perceived AML issue. One bank may consider certain activity risky enough to close an account another may not. Most banks I know will not re-open an account for someone they previously shutdown. You're better off going to another financial institution.

I agree with both of these responses and will add that it may depend on the specific reason for the closure. Banks' risk tolerences to certain industries may change, so if an account was closed in the past because it's a privately-owned ATM, money service business, or even marijuana-related business, there's no harm in asking if their stance has changed. If the account was closed because the bank didn't think the activity was suitable for the type of account/nature of business/occupation, it's unlikely the bank will ever reconsider.