I'm having the same issue. It seems to happen when you do the Add Money cheat while in a shop and not in your inventory. The first time it happened, it duplicated Yennefer's letter, so I just dropped the duplicates. I've just done it again but this time it doesn't seem to have actually duplicated any of the items in my inventory. I've gone through and checked every single one.
If anyone has found a solution to this I would really appreciate it. At this rate my only option is going to be increase my weight carry by 1100 to compensate for the issue.
sometimes you have to scroll down to see the item.
Had the error once too, 10001 bread, couldn't find it either until i scrolled down.
Used the moneycheat on the shop and sold everything to the shopkeep
(i use the moneycheat on shops more than once without problems, it always makes the shopkeeper very rich)
I believe the error is due to a combination of unlimited slot food and the item multiplier
At least in my case.