I run a dinky little private server so my girlfriend and I don't have to play on public ones.
My problem is that mobs eventually stopped spawning on it. It took a while for this to happen at first. I've done lots of research and thought it could be lots of things even just the server lagging, or because at one point I reduced the view distance in server.properties, or that it might have been due to me adding mystcraft and/or damage indicators to our Yogcraft server.
However... rolling back all those things did nothing. I went so far as to copy our world into a fresh install of the server and nothing. There aren't any really laggy things on our world either. We haven't built much more than a house and a few machines, half of which are actually stuck in chests right now instead of running.
BUT, I can get it working again. No change to the configs or anything. All I do is shut it down and rename our world so when I fire it up again it builds a new one. Then I log in once, shut down, and revert it back to our world. Boom... We have mobs spawning again! The only problem is it's temporary. The mobs stop spawning again pretty soon and will only spawn from spawners after that. No normal mobs spawning. Monster spawners still work, wisps still spawn from flux, and I think creatures still spawn in Twilight Forest and The Nether, but none of the normal night/dark spawning mobs in the overworld. I'm not 100% sure about TF and Nether. TF could be just spawners and Nether mobs might just be persisting rather than spawning.
It's very boring.
Any clue why this is happening and how to prevent it? Or at least an easier way to fix it when it does? Perhaps deleting level.dat would be an easier fix? I'll try it next time.
I haven't bothered to copy my configs because they seem pretty irrelevant. It happens even with default configs generated by running the Yogcraft server and never editing them. The only modifications to the server that we still have are Mystcraft and Damage Indicators, but again, I've tried without them and it's the same.
Yes the server is slow, but it's fast enough to spawn mobs for a while and then it just won't anymore. Restarting the server has no effect.
PS. My apologies if this has been asked and answered before. I turned up nothing here in my search and my research so far has only led to things I have eliminated by trial and error such as the reduced view distance thing. I don't know why generating a new world then reverting fixes it when simply copying our world to a virgin server install does not. Logging into the generated world also seems to be necessary as if I just shut down and revert after generating it does nothing. *shrug*