The Hallowfall bonus objective Lurking Below does not complete after using the pickaxe and killing all 8/8 of the worms just remains active.
Same for me, been in my log for 2 weeks and unable to drop or complete
Still existing, I met the completion tasks last week and im still at it this week, it didnt reset on tuesday or anything
I experienced the same bug and saw a wowhead comment for this quest advising to log out and back in while in the quest area. That seemed to work for me.