When the player is shot by a skeleton, or is standing by a creeper blowing up, the item they are holding disappears/is destroyed. This happens with swords frequently, even before they are destroyed by durability level, but it also has happened with stacks of blocks.
Unless this is a supposed feature (it would still be bugged), I think that the player shouldn't have their inventory slot cleared occasionally when they have been shot.
This IS NOT a case where the player may be hitting Q to drop the item, or that the item has been made invisible, but upon attempting to interact with that same inventory slot makes the item reappear. The blocks or items have been destroyed, and I have not been able to recover them.