When mod is installed with the subterranean wilderness mod on Forge 36.0.35, half blocks from the mod are missing sides, leaving holes in the world. I've also posted this issue on the other mod's github, hopefully we can get these two to place nice together :)

REPRODUCE:

Create new instance in Curseforge launcher (Forge 36.0.35)
Install Subterranean Wilderness (SubWild-1.16.5-1.1.2.jar)
Install FerriteCore (ferritecore-2.0.1-forge)
Create new world, find cave

Update FC, this was fixed in build 2.0.2 (but you should update all the way to 2.0.3).