The title pretty much says it all.
The Megalake and Megalake_grove biomes don't appear to be generating correctly, or at all. The biomes sometimes show up on the f3 screen without any lake actually being there.

Here are some examples of the messed up generation:

This was tested in a new world without any other mods installed.

Well, the generation is surely not perfect at the moment, but from your pictures lakes seems to spawn fine. I am aware though that sometimes you find megalake biomes where only ground and glowing grass is generating. However, since i am using the exact same generation algorithm that the Fabric mod uses, i'll have to wait for Paulevs to fix those.