I've been playing a bunch of recovered Nightwave missions back to back in an attempt to get the operator set. The last one I did had me kill 1500 enemies. After completing that one the "Mow Them Down" mission popped up where I had to kill 150 enemies with my primary. I did so, but the mission just keeps coming back. I've completed it like 5 times now and it never gives any points. Now I even have the "Mow Them Down" mission listed twice on the Nightwave screen, one with 23 hours remaining and another with 2 days 23 hours remaining.