Was playing Nuked on endless with one other guy and a (Stand your ground) objective popped up at the start of the wave like normal, the objective was at the back alley (the narrow part on the outside at the back of the map under the arch) once we arrived we stood there for a very uneventful five minutes before we finally realized no Zeds were spawning, it was only after I left the zone that Zeds began spawning.