Over the weekend I got a client request to update an account in their database. FMP16 on Server16. Went into Security and got this message when I tried to update the password. "Admin()" is modifying these items. Made a couple of attempts - same thing. Did some sleuthing and noticed that there were a lot (about 20) connected "ghost" users - all from a serverside script that runs on 30 minute intervals. I disconnected all users then closed and reopened the databases. Now I could make the changes in the security area. I realize I should have done an "FMSE Stop" then "FMSE start" in Terminal to see if that had any effect - next time I guess.
Rather anecdotal to be sure but thought I'd pass it on in case this happens to you. Not even 50% convinced the 2 things are related.