it wasn't me personally but one of the higher up people in my clan said it. He didn't specify how long he was in the missions but he said there were like 4+ hours. And we are on Xbox if that might somehow be effecting the spawn rates.
It should not affect their spawn rate (to that extent). And I've done a few hours long disruption (on PC) and did not notice that. You may ask him how long he was in so I can try to reproduce that if possible.