In my 1.15 redstone world, I had a few designs that rely on comparators getting power from hoppers as items move through them.

In 20w18a When there are hoppers traveling along the x or z axis in a horizontal pipe like fashion, I get power output to a comparator when an item passes through. But if a hopper is leading items down into another hopper, I get no power output. If the hopper is pointed down into any other collection block, chest, furnace, etc, I can get power from that hopper.

In 1.15 and before, I could get power regardless.