Well logically the new zombie spawns should be fine. It's a great idea having them spawn on blocking volumes... but only 1 zombie came. I heard the rest babbling behind the hill... so who knows what was going on
The best thing I think - which I should have explained more explicitly when we were in-game, was: place the Zombie Spawns inside the buildings are around the back of the buildings.
Delete those spawns on the blocking volumes which sadly don't work - and will cause problems if you leave them there.
Then make your red brush 144 x 144 x 144. Move around the map looking for the most hidden places inside buildings to place new zombie spawns and also around the backs of building, even in the middle areas - but close to walls. You'll be placing a whole lot of volumes, but at least when there's many players in the game, zombies will spawn somewhere.
