Hey, I'm getting a bit of cascading worldgen lag now and again when using the mod on a server.
The error looks like this:
[21:58:15] [Server thread/WARN] [FML]: LootGames loaded a new chunk [16, 54] in dimension 0 (overworld) while populating chunk [16, 55], causing cascading worldgen lag.
This Reddit post talks about the issue in case you're unaware:
https://www.reddit.com/r/feedthebeast/comments/5x0twz/investigating_extreme_worldgen_lag/

Thanks for reporting the issue. But for now it can't be fixed until I will make new spawn system. I've read Reddit post, but my structure is bigger than two chunks.

So I'm aware of this issue and will try to fix it in future.