We have a new fullcopy sandbox, created less than a month ago. I've noticed that significant number of users did not get .sandbox_name appended to their usernames. Both Created Date and Last Modified Date are well before the sandbox refresh was even initiated, so I've ruled out the possibility that someone edited usernames on sandbox to match those on production.
Oddly enough, users' emails are changed to email@example.com
Any ideas what I might be missing here?