Can you share with us the name of your bank? This way, I can gather more information about it and provide you the best fix.
Also, you'll want to contact your bank and check if there are any updates on their end. Changes made from them can also influence the connection between your bank and QuickBooks Self-Employed (QBSE) account.
In the meantime, let's manually refresh the connection of your bank to isolate this. I'll show you how:
Go to the Gear icon.
Select Bank accounts.
Click Refresh all to refresh the connection of your bank accounts.