Mobs lagging when engaged in combat

When engaging a mob or group of mobs (ie. Zombie) the game will freeze for roughly 5 seconds and then unfreeze. Doesn't always occur and typically with a group of mobs.

What I expected to happen was...:

The mob would continue forward towards me unless I hit them with my sword and then they would get pushed back.

 

What actually happened was...:

Instead I would hit the Zombie once and then the mobs would freeze for 5 seconds then continue forward.

 

Steps to Reproduce:

1. Find a Mob or Group of Mobs
2. Engage in Combat
3. The mobs will occasionally freeze (I haven't done enough testing to know if this happens all the time)