Iron Golems can wander away from a village even there's 30 - 20 villagers and 20 - 10 beds even they are naturally spawnded from a village or via /summon iron_golem ~ ~ ~ minecraft:from_village

Steps to reproduce

1. Create a new world
2. Expand/find a naturally generated village (not abandoned)
3. Add more beds/villagers (optional)
4. Wait for an hour/minutes for an iron golem to wander away
5. You will see him get pass the village border
6. As it passes do /summon iron_golem ~ ~ ~ minecraft:from_village
7. Wait for another hour or minutes

     You will see the ai is broken