Summary:
Nether caves cannot replace some blocks when generating. This results in no cave exits in some biomes, or some very strange exits.

Examples:

Seed: 4815717814689529847
Coordinates: 87 51 200
Coordinates: -946 52 -1684
Coordinates: -1011 89 519
Coordinates: -995 81 495

List of blocks

• Soul Soil
• Soul Sand
• Crimson Nylium
• Warped Nylium
• Basalt
• Blackstone

Steps to reproduce:

1. Create a world with the specified seed.
2. Visit the above coordinates.

Observed results:
Caves cannot replace some blocks, which leads to incorrect generation.

Expected results:
Caves can replace the specified blocks for correct generation.

Image: