My bank account shows that QuickBooks is authorised and connected, but unable to synchronise my transactions and app asks for reconnection

Hello, useramir-rowaichi.

I'd like to share some steps to help you sync the transactions.

QuickBooks Online downloads the latest available transactions every night around 10 PM PT. Some banks may take a little longer. If you’re not getting the latest data, we can manually update your account by following these steps:

1. Go to Transactions > Banking.
2. Click the Update button.

Here's a sample screenshot for a visual reference:

Once you have the new transactions, you can categorise and match them. If you're getting a bank error code, you can check out this article: Open Banking connection errors. 

On the other hand, you can manually upload your bank transactions.

Please let me know if there's anything else you need. I'll be around to help you out again. Stay safe!