In my case i created a world some time ago on one of the snapshots with new 1.16 biomes and now when i open the world in 20w29a, the place where the soul sand valley biome has generated, now is identified as nether wastes.

I tried creating a new world with the seed of this world (368836386368683368) and when i go to the coordinates where the soul sand valley has been generated, now there's a different biome - nether wastes. As if the game applies what biome is in what location based on the new world generation algorithm (if it has changed?).

I replicated it like this:

1. Create a new world in 20w10a.
2. Go to the Nether at 2, 95, 106 (or any other coordinates)
3. Update the world to 20w29a