Is it possible that this user existed at one time?
Scheduled reports are run on cron. Even though you may not be able to log in as this particular user, you could remove this entry from the apache crontab:
You are correct. Seems this user existed some day. Cleaned up the Apache crontab. This should get cleaned up the moment a user is deleted though imho. I don't know if there is already some cleanup script runngin when a user is deleted and if this could be easily implemented..? If so please create a very low severity fr.