This item has been identified as an outstanding known issue.
Excel add-in 4.3 error "Microsoft is waiting for OLE to complete another action" when trying to create new connection. Error "Unspecified error (Exception from HRESULT: 0x80004005 (E_FAIL))" will also be shown after cancelling/closing out the first error message.
Further updates will be provided here as they are available. If you encounter this issue please contact firstname.lastname@example.org.