Why do you say it is part of the maintenance tasks? How long did they exist within the database?
Removing computers from the SCCM console not as expected (less than 3 months)
Since a few weeks I noticed that some inactive workstations (disconnected from the network) are deleted from the MECM console before 90 days, while in the site maintenance tasks the cleanup of workstations is defined to 90 days
This is not related to manual deletions but to an automatic cleanup action.
What would be the explanation for you?