Short version: Aetherblade Grenadiers on the mortars during Candidate Trials are not despawning with the rest of their crew.
Longer version:
If the Grenadiers are not killed during the trials (I am in the Gnashblade, T4 – but this also happened on T3), when the event ends (failure or success) these grenadiers do not despawn but attack. If the player flees, they will go to the central defense area and stand around with the First Mate. If a player wants to restart the trial, or move to the next tier, they are forced to engage and kill these mobs.
This was obviously less painful on T3, but I just failed a T4 where I had knocked the mortar-guys away from the mortars and they’d been replaced. When I failed the event (less than minute left and just got overwhelmed with mobs that would not leash back to center), the grenadiers turned on me.