In Remix, there is an Ensemble with the itemID 215281 that Wowhead says unlocks the set #3407 (click on the “Use:” line, check Effect #1) but that set is already covered by the Ensemble with the itemID 215279
Ctrl+Clicking the Ensembles also show the same appearances.
I used the Ensemble and now both are hidden on the vendor (because they’re learned) - sadly I forgot to check beforehand, checking the appearances with ATT now shows I know all the Wasteland Ringmail appearances each - however, from memory and per my old account data on the PTR, I bought these from the vendors from original MoP.
So, the set was apparently not learned, as C_TransmogSets.GetSetPrimaryAppearances(3409) gives the sources of the Jade Guardian items.
To tl;dr, the item #215281 seems to teach the wrong Transmog set.
Multiple of the ensembles can not be used when purchased, either.
Ensemble: Tian Monastery Clothing x3
Ensemble: Sun Pearl Cloth x3
Ensemble: Vestments of Serenity x3
This seems to be an issue if you have previously made Pandaren characters and levelled them through their starting zone to acquire the transmog appearances for these ones: despite the Timerunning Ensembles being classified as “Cosmetic” and, therefore, available for transmog on all geartypes, because you have the Cloth, Leather or Mail/Plate versions of the outfits already, you are unable to use the Ensemble item when purchased, effectively locking you out of nine (9) full transmog sets/recolours.
Sadly, your issue is not the only one related to these ensembles, and multiple other ensembles are also having issues with learning them.
Having the exact same issue. From what I can see in my collections tab, you’re correct in assuming it should be the white recolour - my hunter has everything else ‘complete’ but that one has huge gaps despite using the ensemble.