Small tiny, tiny issue. A condi user can kill the blighted avatars spawned by mordremoth after they go invuln and/or after they become your ally, thereby bugging the instance.
And mordremoth can proceed to destroy a section of the platform underneath the rift also blocking progress, occurred when my glider failed to activate in mid air and I was stuck in his AoE, then respawned.
You can lifesteal him to death though, so you know, at least magi gear can stand still and eventually finish the fight.