So I have had this problem for sometime but haven't been able to fix it. This user was able to post in admin only sections, but when I look in the admin panel, I can't seem to find the user. Is there any reason why this is happening?
Please take the regular security precautions. Change all of your passwords and enable two factor authentication for all admin accounts. The fact this person can post in admin areas and that the account is being deleted may be an indicator of a bigger security breach. You may also want to change your hosting control panel, FTP/SSH/SFTP, and similar passwords. Do you have any more data on the user?
I have checked the admin log, and I see no indication of anyone's account being deleted.
Also I may have mislead you guys with this, but what I mean is I set permissions so only admins can post in new and update, but this guy is able to post in there.