Vehicle moving

Hi, I'm working on a takistan life map and well our convoy(for those who don't know it's a ural truck that spawns with AI in it and it has to drive to a base from a spawn position and civilians etc can intercept it) works fine when there's a few players on but when the server starts to fill up the convoy won't move out of it's spawn position until a person goes near it, sometimes it dosn't move even if someone goes near it. I'm very confused as to why it does this.