Completing "The Heist Job" for Vex, I had to hand in a gold necklace which I had stolen and was in my inventory.
The gold necklace looked completely ordinary but cannot be removed from the inventory.
When I handed the quest in however, I ended up with two gold necklaces in my inventory. This confused me as they were marked as favourited but I assumed I must have picked up another and accidentally favourited them without noticing. 15 minutes later however, I noticed that my enchanted gold necklace which I've had for ages (renamed to Sword Necklace) was gone from my inventory.
I've jumped back and forth between what saves I have and I can only conclude that the enchanted necklace had the enchantment removed instead of the proper necklace being taken from my inventory.
This was reinforced when I found this thread on steam which seems to be exactly the same issue:
https://steamcommunity.com/app/489830/discussions/0/3426698343832225879/
I have attached a save (and the skse file whatever that is) from just before the quest hand in. Trying it again I just see the wrong necklace being taken from my inventory rather than a second gold necklace appearing so maybe I was wrong about that part but it definitely removes my enchanted sword necklace instead of the quest item.