Even though this is a super annoying bug, here's how I managed to get around it: 1. Open the transmog menu. 2. Navigate to the piece of armor and the appearance to be unlocked. 3. Place the cursor over the item you want to unlock. 4. Wait. Wait until the on-hover tooltip changes to tell you that you can now unlock this appearance. 5. Press and hold your mapped unlock button. The progress bar on the bottom of the tooltip should complete. 6. Keep holding down the button. 7. After some more waiting (your mileage may vary here), the appearance gets unlocked. I can't really deduce how or why this works, but it's almost as if there is a polling error with the database somewhere.