Magma Cube Bug

I was being silly and just spawning magma cubes like crazy. Then suddenly everything got really slow and glitchy. I wondered what would happen if I spawned an insane amount of another mob, so I left the area to spawn a bunch of chickens. The system got better and less slow. When I was spawning chickens like crazy, the game didn't get glitchy. So I went back to the magma cube area. It got slow again! I went back to the chicken area. It eased up. Back to magma area. Its slow!
(Also, this is version 1.16.201. I had to make it 1.17.0 for it to let me give you this report).