To investigate this case we need more information, could you please send us the Advanced Log?
You can find a short tutorial on how to do it at https://sqlbackupandftp.com/blog/how-to-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.