A bunch of wierd things happening recently, common spawns, ect..
IT seems like horde spawns are totally messed up lately.
DCenter1, at the bottom of the elevator no horde spawns or it will spawn up above the elevator and they all cram together, so you can walk through the map after that point with no commons at all attacking you.
HardRain2, at the elevator fight, no horde until the very end when the elevator arives, then all the horde magically appears in the elevator itself all at once.
There are other spots as well, but I can't remember right now.