Soul Sand Valleys overwrites the top layer of the terrain and turns them into soul sand or soul soil, despite the bottom layers not being soul sand/soil.
Seed: 3264540676790285439. Coordinates in screenshot. Relates to MC-199004, MC-199006 and MC-199007.
Gravel patches only generate on the top layer sometimes
Basalt Deltas only overwrite one layer of blocks into basalt, looking slightly unnatural
New nether forest biomes replace the top layer of blocks with the respective nylium block, even if the blocks being overwritten aren't netherrack; leading to unnatural looking terrain