When creating a new world and going into the nether the Crimson/Warped/Soul biomes are glitched.

In those the ground is only made of Netherack. No Nylium nor Soul Sand/Soil. Basalt Deltas and Nether Wastes generate correctly. 

I've tried to create another world and got the same issue.

What I expected to happen was...:

Biomes should generate with all the correct blocks

What actually happened was...:

Warped/Crimson Forest & Soul Sand Valley didn't have Nylium, Fungus, Soul Sand/Soil.

Steps to Reproduce:
1. Use the last snapshot (21w37a)
2. Create a new world
3. Go into the Nether