One Issue I've found is that sometimes, when you buy a lot of items (mostly ingots), they all seem to get spawned in the same position and explode out when you open the box.
this causes them to fly in the direction the bottom of the box is pointing, presumably because the game applies a little bit of force "downward" to get the items to lay on the ground on unpacking.
When you unpack a box inside your shop, the items sometimes just jam themselves into the floor because of this and are unrecoverable, even by rotating them.
Perhaps change it so the deliveries get spawned in the middle of the box, so they have space to move downwards and hit the floor, or change it so every box has limited space and spawn locations for every item.