Items randomly vanish from inventory
This has happened to me personally 3 times now when attempting to make arrows, both the heads & shafts would vanish when i am crafting the threads.
Others online have said their items also vanished but not specifically related to arrows.
Someone from the Alpha 1 said this was to do with pressing the Enter key, specifically the num enter key.
It causes random item slots from inventory to be cleansed. more items you have the higher chance you have to losing items.