I just added spawners in my start zone and the next zone and they spawn fine, but after a while they all just start dying off completely randomly after following me for a little bit?  ??? It's really start to piss me off as I have no clue why they're doing this - the zones and pathing is all fine I'm 100% sure it's nothing to do with that. I saw on another forum someone had a similar thing and it was due to the areas being too low and he fixed it by raising the whole map up in Radiant, however although the areas are indeed quite low I tried this and the problem still wasn't fixed (also that messes with all my decals and patches and textures and stuff). Any ideas?

The code in question for the "level being too low" theory is this, from _zombiemode.gsc::round_spawn_failsafe():

		//fell out of world
		if ( self.origin[2] < level.zombie_vars["below_world_check"] )
		{
			self dodamage( self.health + 100, (0,0,0) );	
			break;
		}

level.zombie_vars["below_world_check"] is set to -1000 by default, so it is very easy to have your level be low enough to validate this check. I would change this line in _zombiemode.gsc to a much higher number (maybe -10000):

set_zombie_var( "below_world_check", 				-1000 );