Dropped blocks and items

I dropped all items and came back to get them 1000 blocks away I go to pick them up, and they all dissappear within 1 min. After I try to get them, and I swim in a lake, I dropped items and then go to pick them up, there was a sand block floating on the water I couldn't pick it up after I picked up all items I log out and log back in, and I see the sand block floating to the top of the water,  I go to pick it up and instead of picking it up I swim through it, without picking it up, I'm supposed to pick up items if I have enough space for it, its not supposed to be a floating ghost item, and items aren't supposed to despawn after 1 min.