Zombies Won't Navigate?

Me and a friend had a complete fort on gm_construct. Turrets, Windows, etc. But, when we turned on the NPC Spawners, the zombies did not want to navigate towards us. They’d wander around and get stuck on the walls. I was just wondering if there was any way to make them come towards us any better, rather than just walking around in triangles near us.

Create your own map and put nodes in it.