This happened to me if I activated it outside of a gwent game. It would also give me a full toxin bar, but if I only activated it during a gwent game and deactivated it before I left the gwent game it worked great.
Usually just pressing F11 again then refreshing the Inventory screen will show all the items again. You shouldn't have to restart the game or trainer again.
Right (SOLVED) thank you for the TIP on the F11 key for playing the card game Gwent the answer is when you want to play Gwent at the point of play PRESS F11 key then play Gwent, when card game is over press F11 key again and all is well, inventory is fine do this every time you want to play Gwent.