It looks like hung sessions. Can happen sometimes if you have a user who's a little too friendly with the hard reboot (Ctr-Alt-Del), or if your network is wonky. I've also noticed that the new "reconnect" feature is a little iffy sometimes; it can leave sessions on the server after the attempt to reconnect fails.
I would start by checking with the user and find out what's happening. Usually, you can reboot the user's machine rather than the server. If that doesn't help, have your network checked for bad hardware (look for lots of dropped packets with a network analyzer).
I'd also look into getting this user's FileMaker client updated. He's three v-revs behind. Might have something to do with it.