[MC-236646] Major performance decrease when exploring chunks in 21w37a

The Bug:

Major performance decrease when exploring chunks in 21w37a.

This issue did not occur in 1.17.1.

Steps to Reproduce:

Enter a world in 21w37a.
Press F3 + ALT.
Explore some chunks.
→ ❌ Notice how there are major performance decreases when exploring chunks in 21w37a.

Expected Behavior:

The expected behavior would be that no major performance decreases would occur when exploring chunks in 21w37a.

Linked issues

Can confirm.

I've attached two videos that compare what the behavior was like in 1.17.1 and what the behavior is like in 21w37a.

[media][media]

Can also confirm. Chunk loading causes tremendous lag spikes, with FPS dipping down to >25.

Chunk loading is also much slower than in 1.17.1 (MC-236695), which might be related to this issue.

In my experience, the problem seems to be far worse in deep ocean biomes than in most other biomes.

Turning biome blend in video settings completely off can improve performance (that is if you have it on or even high).

Experiencing this as well on a high end setup

This is not an indication of a specific performance problem.