Custom variant mineshafts not spawn as intended. In spawnchunks I am getting a mineshaft made of air, if I am using modded blocks. (Darker Depths in my case)
The issue looking like this and so far appearing only in spawn chunks:

And this is how it should looking, and looking outside of spawn chunks already:

Log files when issue is happens:
debug.log
latest.log
Sometime crash report:
crash-2021-11-25_12.59.20-server.txt
The configs (.txt for github only):
bettermineshafts-forge-1_16.txt
variants.txt

This was likely an issue with how I initialized blocks from the config. Should be fixed in 1.18 but feel free to open another issue if it persists.