Walking in Shadows

(In Remix)
Four Horsemen's Aid Received :

After a minute or so the "diamond" floating above the table in front of the 4 horsemen was clickable. Clicked it.
No Dialogue or sounds. Like nothing happened.
2 minutes later, the 4 horsemen used colored rays on the "diamond".
"Diamond" became interactable again. Clicked it again.
Aid received!

I was really confused, but waiting did the trick for me.

edit: afterwards I used the ghoul on the landing platform, he flew me back to Dalaran

Unlocking a hidden artifact appearance awards the Feat of Strength Hidden Potential. I was awarded this upon turning in this quest.

I gotta say, this was by far my favorite scavenger hunt in the game to date (yes, even the fishing grind). Blizzard, thank you for paying homage to all the red herrings in vanilla! I may never have the original [item=22691] but this is a pretty awesome consolation prize.

Since the quest is back in daylight again with Legion remix...

Once you've bought the shard of darkness from the remix battlepet / toy vendor Horos (100k bronze) and talked to Lord Maxwell in your class hall.

DO NOT FLY BY YOURSELF AND TALK TO LORD MAXWELL AT ACHERUS ! take the fly from Dalaran to Acherus at the NPC.
The game didn't stopped me from doing the further steps of the quest while the first one " Fly to Acherus " wasn't completed, preventing me from returning the quest even if the event was over.

Not sure about the fix since i did multiple things so here are the steps i followed to get the quest to work again:

- Re-logging ( didn't worked at first, maxwell was still in the middle of Acherus with all steps completed)
- Delete quest and relogged in class hall ( still didn't worked, same effect but he was now telling me to talk to him when ready while i couldn't interact with him... )
- Went back to Dalaran, deleted the quest again then re-logged and it worked... ( do it at Dalaran not in class hall or Acherus)

My guess is that since i left Acherus and didn't enter Paladin's class hall, the NPC was able to reset but it might also be a timer since it took me around 10mins because i was looking for infos about this bug.
You won't need to buy the shard again since the game knows you had it

Maybe they'll fix this but it still can happen to anyone so hope this helps one day !