Hoppers with Droppers above will delete Item Entities if routed through Item Elevator

• Create an item elevator (as shown in the uploaded picture).
• Build a hopper chain with a dropper on it through the item elevator (also as shown in the picture).
• Put items in the bottom chest, place yourself at the top of the item elevator. You will receive less items than you put in the chest and all containers will be empty.

Not sure if this helps, but sometimes you can see the top of an item entity in the dropper (it is a full block, so the item entity apperars dark) and it will disappear under your feet. So I think the items are deleted in the dropper block.