this is been a issue for a long time now in my pack and worlds after testing i confirmed it only happen when quark is installed anyway you could fix this.

Minecraft 1.15.2
Forge 31.2.0
Quark-r2.1-243
like i said tho this has been a issue for a month or two now so version listed dont mean much.
also including my config in case its due to something i changed.

https://www.dropbox.com/s/gi9be8lw098zq4k/quark-common.toml?dl=0

Can you send me a copy of your config?

Never mind, I'm blind.

Never never mind, it's 404'ing, please post it again so I can check it

one thing iv change sense this was made after seeing another modpacker maker do the same and it seem to solve it was Crevices after they where disabled that no more void holes. https://www.dropbox.com/s/3m85jl5kvg43duu/quark-common.toml?dl=0 this config is before that change.

This is duplicated in issue #2228 as an FYI. I posted similar images there for reference.

If you delete the Crevices part of the Quark config (or just delete it all) and let it regen it will fix.

Will need a new world for it to take effect.

Confirmed by Vazkii