Items in GUI getting deleted for no reason

It's not a secret that there isn't a single thing in the world more broken than GUIs in MCreator, but this is really too much. The issue is that I'm trying to make the item in one slot consumed and the item in the other one gain durability meanwhile. Anything I do doesn't matter and the item from the second slot magically vanishes even when I delete every single procedure block containing anything about it. I also have "keep NBT/Inventory" checked on on the blocks that change the block to it's functional form and back. Is there any solution for that? I just tried everything I could think of and nothing worked at all.