Root Cause: The Client ID of the user is not being used when deleting users.
Update to a fix version listed below or a newer version if available.
Fix Status: In Progress
Automic Web Interface 12.2.0 - Planned release date: 2018-06-19
Automic Web Interface 12.1.1 - Available
Delete the user in the proper client, where it was created.
Delete restore from the recycle bin works in cases where the wrong one was removed.