Valsirenn got stuck mid quest in the Undercroft Great Hall three times. When I entered the Great Hall the first time, other players already started the quest and Valsirenn got stuck at the top of the broken stairs. I left through the door and reentered the Great Hall which caused Valsirenn to move down to the pearl (after I destroyed it). However, this second time there were other players mid quest and once the pearl disappeared, Valsirenn was stuck working with a non-existent pearl. Once again, I exited the Great Hall and reentered, which finally caused Valsirenn to finish the Great Hall portion of the quest. But, during this third time the pearl never reappeared (there also was another player in the Great Hall).