Hello there, @mbpros. Let's figure out the cause of why your bank accounts are being disconnected in QuickBooks Online (QBO). 

Usually, this will happen once your two TD bank accounts have the same login. If you connect your personal bank account, your business bank account will be disconnected, and vice versa. To prevent this, note that you can only connect one bank account in QBO and manually upload transactions for the one account. Beforehand, make sure to switch to an Accountant view before following the steps below.

1. In Transactions, choose Bank Transactions and select the account blue tile where you want to upload your transactions. 
2. Click the Link account dropdown and hit Upload from the file. 
3. Take Drag and drop or select files then select the file you transferred from your bank, then click Continue. 
4. Select the account you want to upload the transactions in the QuickBooks account dropdown and choose Continue. 
5. Pay attention to the onscreen process of matching the file columns with the correct fields in QuickBooks and choose Continue.
6. Decide what transaction you wish to import and click Continue, and Yes, then select Done. 

However, if your bank account has different login credentials, checking any notifications or alerts regarding this issue on your bank website is recommended.

On the other hand, you need to match your bank statements and your recorded transactions in QBO by reconciling. With this, you can check this link to help you handle further your account inside QBO: Reconcile an account in QuickBooks Online.

I'm ready to back you up if you need more help with your bank connections in QBO. I'll keep the thread open so you can comment back. Keep safe.