Put the summary of the bug you're having here
What I expected to happen was...:
Hit an Enderman with my Iron Sword
What actually happened was...:
When I hit him, he played his creepy sound and then he teleported far away and became neutrual and were I went to hit him again the same happened
Put a step by step guide on how to see the bug by alone
1. Find an enderman in Survival( Be creative spawn one and /gamemode 0)
2. Try to hit him with a sword
3. See what happens
Is this in daytime? Running away is the intended behavior for Endermen in daytime, it only chases you during nighttime.