First, I'd like to know if there's a specific error you encountered. That way, I can share accurate steps on how to fix it. You can also check this link that shows the possible banking errors and their fixes: Open Banking connection errors.
Also, it's best to check with your bank to see if they are having issues that can prevent the connection.
We can also go to the Gear icon and select Connect bank. From the Bank accounts page, click the Refresh all button. This can fix syncing errors and will download the transactions.