I've been having this problem with FMP Server since version 13 and now see it on our v15 test server.
Server is running Windows 2012 via VMWare.
Frequently I have to restart adminserver with command line in order to close databases with Admin Console.
After restarting adminserver the databases close successfully. However going to Status and attempting to turn off the FMP Server with the blue/grey slide button, the slide button changes back to 'On’ again quickly after the slide button initially shows as ‘Off’. I have to turn it off twice for it to stick.