Spartan Ops "Rally Point" mission glitch

Was just playing a game of spartan ops on the aforementioned level, and couldn’t complete it due to the last enemy of the wave spawning/glitching inside the ziggurat thingy at end of the map where the level starts. Even after ages of lobbing everything left on the map at the approx location of the dot, could not progress with the mission because it just couldn’t be killed! After a while bits of it started poking through the wall, seemed to be a Promethean watcher. Even the sticky out parts couldnt be harmed though, and it would just go back inside the wall.

Annoying, but has only happened the once, so wonder if anyone else has had problems with unkillable enemies ruining the game?