On Melody results page (/arctic/advent/select-years), hovering on mobile resulted in no popup except an "No Item Found" bar in red text.
Kumos inventory page confirmed I had the items, but when opening one directly from my inventory, the information provided said I had 1 copy (in inventory) and failed to recognise the one already in my wardrobe. When I therefore clicked "move to wardrobe", it seemed to work, but then was still in my inventory.
I had to return to the main site to verify that I do in fact have two copies now, and that's why it wasn't going to my wardrobe.
Using FF145.0.2 on Android 12 OS Item not showing other copies was: [item2=Oh Deer Nose Cap]