The hidden artifact appearance " The Bonereaper’s Hook." Seems to be currently unobtainable. I did some digging on wowhead and via the Death Knight community discord and the tribal knowledge would seem to be that this has been the case for some time.
As far as a good repro goes there is a way to get the quest needed for the Hook listed on wowhead that I tried myself to no avail probably 100 times, and some people i have spoke with say theyve spent days doing this with no luck: https://www.wowhead.com/item=139548/the-bonereapers-hook#comments:id=2377872
LMK if I can get you logs or something
Thanks