When joining a superflat world/creating a superflat world/crossing a chunk/respawning, a massive amount of lag is generated

I was in a superflat world generated in 1.16.2 pre-3 and that happened
I tested this with other types of world generation (The default/Large Biomes/AMPLIFIED/Single Biome/Caves/Floating Islands/Debug) but they didn't have the same issue
I also tested this without structures and it was the same issue

I have videos showing ways of reproducing this bug

Note that the biome in the 1.16.2 pre-3 superflat world is "ocean" whilst in vanilla 1.16.1 is "plains"