C2ME-forge - https://github.com/ishlandbukkit/C2ME-forge/actions/runs/866624292

As short, this mod designed to improve the performance of chunk generation by taking advantage of multiple CPU cores in parallel.

So, with C2ME - bettercaves doesnt generating.

Another generation mods working very well.

I would consider making an issue with the folks over at C2ME. I plug into the cave carving system in a pretty conventional and compat-friendly way. It's hard for me to help you since I have no idea what kinds of changes C2ME makes under the hood.