Yes it was here After shutting down a container, backup.yaml appears in the mount directory
The OP struggled to get debug logging working as he was encountering a separate snap issue that prevented it from being activated, so we never made any progress with it.
@Tomas please can you enable the debug logging and paste the output here from starting and then stopping a container to recreate the issue, as I’d like to see what order the mount and unmounts are occurring.
Thanks