When you set items in your hotbar and go to press them, (1, 2, 3, etc.) the item is not brought to your hands. The hotbar "wakes up" and you can see the items, but you have to press the number multiple times (sometimes up to 10 times) to get the item to actually go to your hands. Going into your inventory and manually moving the item into hands works immediately. Also, as I mentioned, the hotbar reappears after having been gone for some time, so the game is registering that you are pressing a hotbar key. But it does not move the item to hands until after multiple key presses.