How to make a recovered machine recognize its subscription?
When you recover a physical machine from a backup, a new machine identifier is created. Therefore, the machine is not able to back up to the subscription it used before recovery. This happens regardless of recovery to new or to different hardware.
To continue backing up the machine to the same subscription, reassign the subscription to the machine. If you do this, the next machine’s backup can be incremental. If you assign a new subscription to the machine, the software will have to do a new full backup.