I was doing a random dungeon, it required 2 chains to be released. I had released one but died trying to get to the other; I was resurrected inside the locked door area , i could not open it from the inside. I thought I had somehow luckly by-passed a 30 second fight… and continued into the dungeon and killed everything in there, quest state still said " open last chain " or what ever. Once I had killed all the monsters and blisters, I realized I could not progress.
Re-entering the dungeon and opening the last chain did nothing, the quest info just went blank.
In short : I died and resurrected inside locked quest area, quest could not be completed.