Deepslate doesn't generate on the new caves in old chunks

When generating caves in existing chunks on the new snapshot, the caves generate with stone and tuff on them and not deepslate. You can only find deepslate where the bedrock layer would generate in the old world generation.

How to recreate:

1) Open a world created in 1.17.1 or below in the new snapshot
2) Check the caves below y0 on chunks previous loaded