The bug

Iron golems rarely start spinning and wandering around aimlessly, even when aggravated, if the player hits them and is killed by them repeatedly.

To reproduce

1. Create a new creative world.
2. Go to a village (might not be necessary) and spawn iron golems using /summon iron_golem.
3. Switch to survival mode and set the spawn nearby.
4. Hit the iron golems and respawn repeatedly.
5. The golems will eventually start spinning around and wandering aimlessly, even when aggravated.

Note: dying/respawning is required to reproduce this issue. I tried to reproduce this by giving myself Resistance V and I consistently failed to do so. This is also incredibly rare, so it will probably take a long time to reproduce.