unpreadictable

Also it only happens in the nether. Im playing right now and nothing is happening in the over world.

So i have a private port forwarded server with me and and my 3 other friends playing happily together. Im messing with circle magic from the witchey mod. And they are messing with Necromancy. At some point i need more quartz. So i go to the nether! And guesss what I find? Huge lag spike, 100 mobs spawning all at once. 40 ghasts spawning. AND crash. I reload. Use the kill all mobs command (dont remember what it was) And i go on. POOF they spawn again! And again and.....again. Someone know what could be the problem or atleast a way to fix? Thanks.