Cannot Transmog my PvP daggers into any appearance

I’ve had my entire Bloodfang set on with my PvP daggers Transmogged to the House Renethil cosmetic for some time now. Today I went to change everything into something different and tried to transmog them to the Fangs of the Devourer appearance that I had. Didn’t work. Ok. Disabled all my addons, restarted the game completely. Still didn’t work. Tried another appearance off some random drops. Still won’t transmog. I assume that its now broken/bugged since it won’t let me change the appearance to anything now.

EDIT: This is for my Rogue, not my DK. Just happen to be under my DK here.

EDIT 2: Ok so the House Renethal Ceremonial Dagger cosmetic that I bought has completely disappeared from my collection. Which because my daggers were previously transmogged to that appearance, I can only assume that is what is causing the issue. The cosmetic was sitting in my bank and now its sitting in my bags and I still don’t have the appearance. So does this have to also do with me being in the Venthyr covenant before and now because I switched to Kyrian its completely bugged the transmog system? Either way I need this fixed please so I can go about my business. I either need the appearance restored to my collection or a refund of the Anima cost so I can go rebuy it or something.

EDIT 3: Clearly it has to do with Covenant Switching. Can't Transmog Weapons After Switching Covenants

Please Fix This!