This has been happening to me ever since I started making custom items with commands. I make an item with a command generator, then I hide it around the map in chests or put it in villager trades. Sometime later, I enter the same command I did before and it doesn't stack with the items that already exist within the map. This same issue has been occurring to me for years now. I decided to try and look into why this is happening, and it seems that the item has somehow changed its data. Item 1 represents the items that I have already placed in the map. Item 2 is a fresh item that I just made by using the SAME command I used for it originally. I highlighted the area that seems to have changed with a red box. Please help, this is making me go INSANE!