You have a machine with a backup plan. In a while, you re-register the machine to a different user, but the backup plan still runs although it is not listed among backup plans for this device. If you delete entries about this backup plan via acrocmd, they return in a while.
Issue is caused by current limitations of the Backup Plan design. Current design makes the old backup plan invisible in the old tenant's Backup Console, but still sends commands to the machine to apply the backup plan.