Not configuring a cleaner schedule could also impact the cleaner full cycle completion
So current functionality The cleaner will auto start during system idle time. Once a backup starts, the cleaning process will stop, not completing it's work. So if there is no full cycle completed it could add to pending work. Pending work mounts and that is part of the reason for the message.
Recommended actions:Set a cleaner schedule to allow the cleaner to run full cycles.