.. then the door homing missiles were introduced, aka regular zombies. I gave this a shot more than once with A19 and the only way to somehow sustain is to make sure there is no door and try to make them spread out, so they don't get the idea to focus on one weak point. YouTube also seems to revolve around cheesing horde night.
For the love of this game, just remove this stupid mechanic and make them come in from all sides again as it was.