Hopper taking/giving inconsistent amount of items

I have a hopper that powers the hopper underneath it until the top hopper has more than 68 items (signal strength 5). The hopper should then let one item through to the bottom hopper, but instead lets 2 items through. This persists, but sometimes is solved by reloading the game. Where in the fixed case it takes a single item as it should.

Video showing the issue: https://www.youtube.com/watch?v=Gn_ztnbGyNk

Attached: Multiple of these setups, where all work (after reloading) except the one closest to the player (north most one).

The fact that the setup does not take items from minecarts is beside the point.