To investigate this case we need more details. If you still have this issue, please open "Advanced Log" window, and make sure that "Log enabled" is enabled, then run the backup job to reproduce the issue.
After a backup job is completed and the issue is reproduced, please open "Advanced Log" window and click "Send log to developers".
If you cannot reproduce this issue, please send us the full log of the backup job where you get this error message.
To make your logs private, please send them to firstname.lastname@example.org
Sorry for the inconvenience.