Hi there, joy-nguyen.
May I know the name of your bank so that I can check if there's a reported issue between QuickBooks and your financial institution? Is there an error message every time bank disconnect?
You may try logging in to your bank's website and check if there's any updates or undergoing maintenance. This might be the reason why it keeps on disconnecting.
Keep me posted how it works, I want to make sure that you're able to connect your bank account to QBO. Have a great day!