Hey,

In Forge 1.11.2 - 13.20.0.2258 there is a new detection and log for worldgen features that load new chunks and cause more worldgen.
This can cause a lot of lag when loading new chunks. I wrote a post about the issue here.

[Server thread/WARN] [FML/]: Actually Additions loaded a new chunk (-6, 12 Dimension: 0) during chunk population, causing cascading worldgen lag. Please report this to the mod's issue tracker.

You can debug this by grabbing the latest Forge, creating a new world or flying around, and putting a breakpoint at this log (at the bottom of Chunk.java). You should see that one of your worldgen features is loading a new chunk and causing more worldgen.

I hate world gen

Apparently my fix for it was still slightly wrong. And there was much easier way to do it. Does it actually work now? I remember it shouldn't be that easy to fix this generator. And I spent much longer than expected to "fix" it and the way I did it was weird and hard to understand (and I initially reported it as issue #275, before forge warned about it)

It's fixed.

I'm almost sure that lush caves don't generate 100% correctly now. Unless there is some magic besides what I see in this commit, or someone reverted some of my other changes in the meantime..

As I already said, the issue is solved and lush caves are fixed.