Orphaned classes can be an unexpected result of suspending or deleting a google account.
When an account is deleted in Google you are prompted to transfer user data to another user. This does not include Google Classroom classes, so any active classes owned by a user who is deleted enter an orphaned state, showing as “Unknown User”. The class can no longer be updated because google cannot update a class owned by an unknown user.
How to prevent orphaned Classes:
If a leaving teacher owns classes, it’s recommended that you transfer ownership to another teacher or a placeholder account (maybe your admin user?) Just add another teacher to the group in smartadmin and set the new teacher to be the "Main Teacher" Hit save and the Classroom Owner will become that new teacher.
In this screenshot you'll see Smart Mentor is going to be set as the new Main Teacher. This will set Smart Mentor as the Google Classroom owner.
How to restore orphaned Classes if you have already deleted the google account:
If a teachers account has already been deleted in google admin just search for the user in google admin > recently deleted users and Restore the users account.
It can take 24-48hrs for the account to become fully restored and google classes to re-link. Once the account is re-active you can sign into smartadmin and change the Main Teacher as explained above- The new Main Teacher becomes the new owner of the class and the class can be used again.