Mobs jitter and slide in crowds when they cannot reach the targeted player

Short description of the issue
When a crowd of mobs is targeting an unreachable player, instead of smoothly crowding around the player like in previous versions, they now erratically jitter, snap around, and bounce off of one another.

Steps to reproduce the issue
Place a large number of mobs into a pit below a survival mode player. They begin to exhibit the incorrect behavior.

Expected result
Mobs smoothly gather around the player.

Actual result
Mobs jitter and bounce off of one another.