During the broodhold, in the large room where 3 worms need to be deposited, there is a glitch where worms disappear. It seems if the barrier knight uses his shield twice, it will despawn the worm shortly after it is dropped. It is very frustrating in the grandmaster to have to start over. Let's fix this quickly bungie.
It happens when you also accidentally step on it after completing a finisher and when an explosive thrall blows up to close to it.
If either of those two things happen you then need to go to orbit as a replacement barrier knight NEVER spawns.