When you have a high number of mobs in 1 by 1 area they will appear like getting out through the blocks.

Expected result:

Mobs will not move out.

Actual result:

Mobs glitch out and appear like flying from their place.

How to reproduce

1- use blocks to create 1 by 1 area.

2- add at least 50 mobs like zombies for example (using mob spawner, spawn eggs or commands).

3- add more mobs or killing some.

This affects players when AFK-ing near by a mob spawner. Players design the spawner to fit mobs in a small area.

Note: hostile mobs will not try to attack the player.

This bug did not appear in the last update.

Attached a video showing the bug, and a picture from my survival world showing spiders freezed in the air.