The only quest item I am missing for this achievement is the amber blade. I have completed numerous time rifts. I have all the mounts and pets. I have most all of the transmog, I have the jingoist set on my main (hunter), just need to buy cloth, leather, and plate. I am 8k from exalted. I have completed quite a few rifts with Klaxxi, actively completed, not sitting afk. I have completed every other quest over a week ago. Still, this one does not appear despite me scouring the area in and out and killing everything. Someone at Blizz Central needs to double check on this item.
UPDATE: finally got it, I think the problem is that its a flat item lying on the ground in water, the exclamation point needs to be made about 5 times bigger so you can see it.