Happens at least once a day. It is noticable during early morning hours when nobody is playing on the server (eg. between 0200 and 0700 GMT+1) and the server has just restarted. Server restarts and gets stuck with an ingame time of 09:20 for at least half an hour, and doesn't begin simulation until a player joins the server.
Note that in the "normal/working" case and using the ingame client browser, server seems to go from 08:00 where it stays a couple of minutes, to 09:20 where it stays about a minute, and then back to 09:00 where it seems to actually start the ingame simulation. But now when the problem occurs, it goes from 08:00, then to 09:20, and then it gets stuck.