Based on the details you've given, we are dealing with a parent-child accounts in the Banking page. With that setup, we can't connect both parent and subaccounts. We can only recommend to create two subaccounts where the bank transactions flow separately. You can check this article to see the details: About bank or credit card subaccount setup. Sub-accounts already created. QBO just does not show new child account as an available option to import.

If you have followed the setup and still got the same problem, I'd recommend contacting your financial institution. They can give you further instructions on how to get through with this. You can also view this link if you encountered bank error within the Banking page: What to do if you get a bank error or can't download transactions in QuickBooks Online. B of A says there is no error on their end, and no restrictions on the account, it's a QBO problem. B of A has reported the issue to their engineering dept.

Lastly, you can reach out to our support if you got a confirmation from your bank that everything working fine on their end. Our support will be able to review your situation further. Support has sent this to engineering.

I'll keep you posted if it's resolved.