The quest name is Skullcrusher the Mountain, in Twilight Highlands. It is the last quest in the zone storyline.
I turned in Hammer of Twilight and accepted this quest, and a cutscene starts. However, the game immediately disconnects and makes the first requirement of the quest, ‘survive Skullcrusher’s backhand’, not complete.
This makes the quest impossible to complete because of this disconnect issue.