Steps to reproduce

1. Load MCPE-151535.mcworld
2. Flip the lever at 2, -59, 17.
3. Wait a while.

Expected results

All of the hoppers fill up in order one after another.

Observed results

Some hoppers fail to grab items passing over, either sometimes or every time.

When items are aligned and on ice and pushed over hoppers by a slime block, there are gaps in relation to the slime block where hoppers don't collect any items.

In the attached picture, the gaps between the hoppers represent the places where they work, while the hoppers in the picture are unable to pick up items.

To reproduce build whats in the picture (comparators are only to see if a item is collected), throw items between the chest and the slime block, and launch them down the ice. If done correctly nothing should be picked up.

This behavior appears to be consistent in all directions except the last hopper, that ones directional. It's also important to note items must be be touching the half of the chest closest to the piston when launched, otherwise theres no issue.

It may seem like a niche issue, but when combined with other hopper bugs, it makes mass item collection in the nether a nightmare.