This bug appears only in creative mode.

If you setup a repeating command block, let it replace an item in your inventory with /item replace hotbar.0 with netherite_sword and spam shift + left click in your inventory on it three times, the item will disappear, but it is still there in your nbt data.

When you replace the slot with a sword a weird effect will appear. If you try to break a block it will make a break sound and particles but it will be replaced instantly by the server because you cant break blocks with a sword. (In singleplayer the server of the singleplayer world)