Put the summary of the bug you're having here

I thought they game would run in normal way

The actual bug is an area that has some kind of mini chunks if about 5x5 blocks, they are all copies of eachother and contantly change (you see dungeons, sometimes trees or ocean Bottoms)

Steps to Reproduce:
1. create a new world with gamemode creative and large biomes
2. i placed down the 4 new blocks of the new underwater structure and removed them
3. After that i killed a bunny
4. then i took goldblocks and made a little surface to put 4 beacon blocks on it in a row, on top of those beacons i put pinkglass, magenta glass, purple glass and blue glass.
5. I flew around for a bit and wondering how awesome the colours are and then sunddenly that bug arrived
6.i changed to spectator mode and flew further to the other side of the bugy area and saw some mobs (bunnies only) and weard dark things with holes in it which were moving and haveing the same flickering bug aslike those chunks, it looks like those thins are copies of the bunnies.