In the Fallen Shield encounter of GoA, I used a devour/lingering nova bomb on a servitor, and the servitor 'ball' didn't spawn afterwards, and no servitors spawned following this, softlocking the encounter. My guess as to the cause is that, since there was a wall right behind the servitor (main room of bottom left island when looking from encounter spawn), the collision of the nova bomb blocked the spawn location of the servitor ball, preventing it from spawning.