In 20w45a I've noticed a bug were nether trees would not spawn in in the terrain of the nether. The only things I've noticed spawning were the ground blocks of the nether wart stuff, and the warped vines, other than that I haven't noticed anything else. (Java) I have screenshots of the unusual spawning below. I have not noticed a single stem in the nether, I've seen the stuff that grows off the stems on the ground embedded.