Just letting you guys know about this...

This happens about every new chunk in my server.

[13:41:11] [Server thread/WARN] [FML]: Dynamic Trees loaded a new chunk [-5, -48] in dimension 0 (overworld) while populating chunk [-5, -46], causing cascading worldgen lag.
[13:41:11] [Server thread/WARN] [FML]: Please report this to the mod's issue tracker. This log can be disabled in the Forge config.

I too get massive cascades to the point my computer freezes completely (I have plenty of power to run this and some)

These errors are kinda hard to track. I have a breakpoint set for when it happens in my dev environment and I promptly fix it. I hardly ever get these errors anymore as I've fixed most of them. Since a proper crash log isn't generated I just have to wait until I experience it myself as there's no telling where the problem originates from.

In what biome do you tend to experience this the most?

i'm getting a lot of cascading worldgen errors too in the foresthills.

Still an issue

I think the fix was to offset x and z by 8 or something, but I'm not sure

Getting this too.