Steps to resolve an issue where a backup that was deleted on the target compromised the other backups in its group.
If a backup in the latest group is deleted on the target then any backups in the same group on the source replicated will create an invalid group on the target. The target should verify that all backups in the latest group has been replicated. If a backup is not on the target then the missing backups need to be re-sent.
Upgrade to version 9.1.0 or later of the Unitrends software.
A known bug in a version previous to 9.1.0.