We seem to be experiencing this very same issue.
Server goes "online".....then 5 to 8 minutes later.....goes "offline".
I remember having a similar incident when using AC15 a while ago.
Seemed like we had a conflict in ports between our messenging (Yahoo messenger) at the time service and AC15.
I was instructed by a fellow GS tech dude...(Nick where are you when I need you now!!!) who was able to resolve the problem effectively by switching out to a different messaging port in AC so that it wouldn't conflict with the Yahoo messenger chat session.
Could someone else shed some light on this issue? why/what is causing our server to go "offline/online" intermittently???? please advise.
...Bobby Hollywood live from...
Archicad 22, Archicad 23
Windows7 -OS, MAC Maverick OS