Hello! I've been playing in both 21w39a and 40a lately and in both snapshots, it seems like the only biomes that properly spawn are the nether wastes and basalt deltas; in soul sand valleys, only structures like fossils spawn, and in the crimson and warped forests, only vines spawn. I'm not sure if this is intentional, but since I can't find anyone else reporting this, I figured I should do it myself! Have a good day!