There was a race while two or more snapper commands were about to mount (or unmount) same filesystem snapshot on same snapper configured filesystem. Usually the race occurred while first command created 'post' type snapshot on a snapper config with allowed background comparison and the second command was trying to access the very same snapshot. Only the LVM2 thin provisioning backend with arbitrary filesystem on top was affected.
As an impact of that race occasionally snapper 'status' command initiated right after the other command triggering background comparison failed with following error message:
# snapper -c my_config status 1..2
With the current fix the mount and umount operations are serialised properly via mutex per each snapper config (configured LVM2 backend).