the monsters disappear

[Chap]

They're set to automatically disappear if the player is out of range and if they're out of sight with no set tasks to do. So basically to stop them despawning you could set up a looping command which sends them to specific nodes in your map or you could set the NPC to wait on a node for as long as you need.

But if they have no scripts assigned to them, then will just despawn because they have nothing to complete and they haven't been told to not despawn. Hope that helps, GL.