I have added Melio for paying bills, which I had been using before QuickBooks online bill-pay changed (increased fees). I also had only been using Melio for paying bills on one particular checking account. After I added a second checking account from which to pay--that is when I began 'losing' addresses from Vendors' records.

I have re-added the addresses as I have discovered them missing. It's just annoying to have to either void the check, edit, and re-print, or, address and use a non-windowed envelope separate from our usual check-envelopes. 

No one else enters or edits this information in our QBO file, only me, so I know it is not a user-generated issue / edit.