I'm running FMPS 126.96.36.1990 on a Win 2008 r2 server. I've seen this twice where I'll open up the Admin Console, click on General Settings > Administrator Groups and no groups appear, despite me previously adding them.
The first time it happened, I re-added the groups. I rebooted the server at some point after that and then it showed duplicates for all the groups. I then deleted the dupes to only leave one of each.
It's doing it again, not showing any groups. I can't restart the server to see if that causes them to reappear because the server is in production.
The groups work though because I was just able to upload and host a test database using a test account.