I appreciate your troubleshooting. Before we check the mobile app, can you first see if your banking transactions are visible when you log in to QuickBooks Online via a web browser? This will help us determine if the issue is specific to the mobile app or related to the bank connection itself.
If you can see your bank transactions in a web browser, your bank connection is good. Transactions may take longer to appear in the mobile app, so try closing and reopening it. If they're not showing in the web browser either, please let us know if you see any error messages. This will help us resolve the issue.