Updated by EVGENSYPERPRO.
Summary:
Updating the world to version 1.21.60 sometimes causes loaded river chunks to regenerate incorrectly.
This does not affect newly created worlds in 1.21.60 and chunks that were not previously generated.

Steps to reproduce:

1. Create a world in 1.21.51 with seed -3763674536482985406.
2. Teleport to coordinates -14 63 -17.
3. Save the world.
4. Update to version 1.21.60.
5. Open the created world.

Observed results:
The generation of the world around you is broken.

Expected results:
Generation will be preserved in both 1.21.51 and newly created worlds.

Original description:
Many parts of rivers are broken in the latest Preview version. I have exported a world from the non-preview version of the game (1.21.51) to the preview version, and when I opened the world, I saw that many river chunks are broken, being overwritten with land instead. It seems like it doesn't overwrite caves, only the water.

I attached some screenshots of 2 different coordinates in the same world in both the non-preview and preview versions showing how the chunks in the Preview are broken in rivers.