It crashed when i spawned 10 /12 zombies

Put the summary of the bug you're having here

*What I expected to happen was...:*Zombies to die by iron golems
Describe what you thought should happen here

*What actually happened was...:*iron golems did not move
Describe what happened here
iron golems stayed in same position after u named them with name tag and zombies moved forewards
Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...I spawned some Zombies i named iron golems
3. ...it crashed