Delay in entity attack

If you have a zombie that hasn't noticed you yet then your next to it and it notices you, there will be a delay to when the entity attacks

 

Steps to reproduce:

 

1. Go in creative
2. Spawn a zombie and you in a 2 by 2 hole
3. Go in survival

 

Observed results: the zombie will have a delay before it attacks the player 1-2 seconds or less

 

Expected results: the zombie will immediately go attack the player