Let's sort out your bank issue, Kelvin. That way, you can manage your bank transactions seamlessly.
There could be several reasons why QuickBooks stopped syncing bank transactions. It could be due to a temporary issue with the bank's servers. That said, I'd suggest logging in to your bank website and check the following:
Check your account for messages, notifications, or alerts.
Look for any display issues as you navigate the website. These can block QuickBooks from downloading new transactions.
Check your bank's website for any announcements about new security requirements.
Once you've connected a bank account to QuickBooks, it will automatically download your transaction data each night. You may also have the option to manually update your account to add any transactions that have cleared since the last automatic download.
Here's how:
Select Banking or Transactions from the sidebar menu.
About duplicate transactions, you can exclude them from the Banking page to get rid of them. Lastly, here are some articles that you can read to help speed up the reviewing process of your online bank transactions:
Keep me posted if you have any other questions about downloading your bank transactions to QuickBooks Online. I'll make sure to get back to you as soon as I can. Have a good day.
Try opening your QBO account on any private/incognito browser. If the same error persists, use MT Online or one of the converter tools (e.g csv2qbo @ $60 one time license) as a workaround.