Items Dropped sometimes disappear

It is kinda hard to describe, but basically sometimes the item in my hand is dropped and disappears. It is then replaced with another item ❓ from my inventory in survival mode (not sure on this one). Reloading the world causes the dropped item to appear in front of me on the floor. I have no clue exactly what happens so that might be wrong but all I know is I keep dropping my pickaxe and having to reload my survival world for it to reappear.