Minecraft 1.16.5, Forge 36.1.0, Atum 2 version 2.2.2, The Undergarden 0.5.1

Atum 2 seems to be using Undergarden Frost Field biome elements (blocks, plants, ambient sounds, etc.) to form rivers. I tried this on two different seeds and it was the same. Just long, thin lines of snow and sand winding through the desert, immediately switching to creepy sounds.

Could you provide some screenshots?
Can't reproduce it.

That's very weird.
I assume you have a bunch of mods installed?
Could you try with just Atum and Undergarden? (And Curios of course)

Issue did not occur with only Atum, Undergarden, Curios, Xaero, and WAWLA installed.
<SPOCK EYEBROW>Fascinating. </SPOCK EYEBROW>

That's very interesting.
Could you provide the list of mods, you originally used? Possibly a CurseForge export, if you have one.

This happens when biomes conflict. There is a mod that is messing up the biome tags.

Thank you for the clarification :)
As we do not use Biome Tags to control our generation at all, we can't do anything about it.

I'd suggest this gets posted on the Undergarden github