The wrong number of "units processed" might be found in the logs after running the CleanUpDatabases task for a database:
ManagedPoolThread #10 12:25:48 INFO Job ended: CleanUpDatabases (units processed: )
The number in the logs appears to be one less than the actual one.
To resolve the issue, upgrade your solution to Sitecore XP 10.3.0 or later.