This is the personal story where you have to go into the sewers and fight the Undead Scout. The bug here is that the walls of the sewers while in underwater combat seem to only be solid for you. Enemies such as the jellyfish and undead scout can swim through the walls so you cannot target them but they can still hit you. Warmaster Forgal also has this magic ability to ignore wall solidness.
It took me a frustrating hour to complete this mission as the undead scout kept getting stuck behind the walls and then resetting once my clones shattered (I was on my mesmer). Forgal was nowhere to be seen as he had died behind a wall to the jellyfish that can also swim through walls.
Attached is a picture of when the Undead Scout swam through a wall and decided to hang back there while I couldn’t hit it.
