Not sure if this is the problem, or not, but in the final screenshot you’re grabbing an array of all of the weapons, then adding an invalid weapon onto that list at index ‘Item ID’. Surely you should be using ‘Get’ instead?
Also, I’m not entirely sure what you’re trying to achieve, but I don’t think that’s going to work. There’s no guarantee that that getting all weapons will return the same list each time, so your index may be invalid/incorrect.