Chunk blending on rivers or by water and in caves is completely broken

Chunk blending by water does not work, as it just shows the chunk borders. This is especially seen in snow biomes

Also chunk blending underground is also broken, especially seen with aquifers as those just get cut off, and there are sometimes just flat walls where a cave should continue.

I have seen this for a while, but I don’t know the exact cause.

How to reproduce:

1.load a bunch of chunks in a world (if looking for river chunks, preferably in a snow biome)

2.update game to newer version, and load newer chunks

Expected result:

Chunks should generate smoothly and newer chunks should blend with old chunks

Observed result:

Caves are cut off: aquifers are cut off, rivers are cut off completely sometimes with newer rivers going in a different direction.

(Btw no addons cause this, as I have seen this bug from before addons were a thing in older worlds, it just wasn’t as severe back then.)