The Armlet of Torug is not one of the relics needed for the Master Relic Hunter achievement. This is because it's possible to finish the quest and NOT contribute it to the museum, instead leaving it at the top of Sorrow's Kiss, by choice. So, it is not included in the 20 needed.

It sounds like what's happened is that the Eye of Zthenganaz is in the museum, but the game believes you haven't contributed it to the museum.

The bug here is as follows:

At some point after getting the "Wrothgar Relic Hunter" achievement (for putting 16 of the 20 listed relics into the museum), the game will believe that ALL 20 of the relics are in the museum, and move them there, and delete them from the places in the wild where they should be.

So you did NOT actually pick up the Eye of Zthenganaz and put it in the museum - the game did that, by error, for you, when you placed the 16th relic and got the "Wrothgar Relic Hunter" achievement.

If you've managed to place another 3 relics, it's probably because you already had them in your inventory, and thus went from 15 to 19 relics placed in one visit, having left the Eye of Zthenganaz for later.

The only solution is to keep on badgering the bug reports until somebody FINALLY deigns to actually reply to you, rather than put your report straight into the "closed - thanks for feedback" pile. Even if you get the automated reply, at least it's a reply: answer back saying that it doesn't fix your problem, explain why it doesn't (i.e. because repeating the same procedure, going back to get the artifact, doesn't work, because it is in fact not there at all). Be sure to include screenshots of the following:

(1) The "Wrothgar Master Relic Hunter" achievement progress, showing the artifacts missing
(2) The missing artifacts, already in the museum
(3) The place where said artifact SHOULD be, in the wild, and it isn't there.