I’m also having problems with this quest. The first time I attempted it, the “explore beneath the broken gate” objective was stuck and never progressed. Just now, I attempted this quest for the second time and the “Defeat the Undead” objective never progressed. I killed the monster, the cut scene didn’t trigger, and I was stuck. During this second attempt, I died once and was reset at the check point, so I’m not sure if that had something to do with it.