when "holding" an item (having clicked on an item in your inventory screen so that it travels with the mouse), if you press F6 to start broadcasting to twitch (this bug occurred when a twitch account had not been connected) the item you are holding will vanish. if you press esc (or probably E as well) and close your inventory it drops on the ground. however, if before exiting your inventory you pick up another item the "invisible" one does not drop and is destroyed. This occurred to me with a damaged iron pick first. I went into a creative world and it happened there too, with a stack of a few levers. Right clicking onto another item of the same type (so that they can stack) makes the invisible items come back. I tested for a few minutes and there does not seem to be a way to duplicate items this way. I checked because when an issue can make items disappear, it might be reversible and make item appear.