Items disappearing from world after leaving

I mined about 6 and a half stacks of iron yesterday and smelted it most of it before I left. When I left the world I collected most of it and left some to smelt. When I got back on today the only iron I had was the ones I left smelting in the furnaces. Neither me nor my friend have the right amount in our inventory. The only picture I have of the iron I had shows 2 stacks and 5 raw iron. The armor I'm wearing was made before I got the iron.