https://paste.gg/p/wphant0m/6a02ed1f151f4b5a92f39c309637fe0e
Seems to cause a crash randomly as in, I've got no clue when it crashes, it just does. Something to do with the saplings?

I can replicate by growing both "Forbidden and Arcanus"s sapling with bones meal in single player. Doing so does not crash the internal server but world generation thread does (it's just a little harder to replicate).

forge: 34.0.13
Forbidden-Arcanus: 1.16.3-1.0.0
note: clean install, with only forge and Forbidden-Arcanus

Was fixed in 1.16.3-1.0.1