When a hopper pushes an item into another hopper that already holds some items, it does not reset that hopper’s transfer cooldown.
When a dropper or crafter pushes an item into a hopper that already holds some items, it does reset that hopper’s transfer cooldown if the hopper is locked (powered) at the time. This is inconsistent, and limits the use of redstone to time the interaction of droppers and crafters with hoppers.
Clocked dropper+hopper fail.mp4
Crafter sequence fail.mp4

Steps to reproduce (in 1.20.41)

1. Load Dropper_crafter -_ hopper bug.mcworld. It contains 6 test stations labelled A-F. Each consists of hoppers and droppers and redstone timing mechanisms that control their operation. The hopper at the left of each station is the output. A comparator in front of the output hopper shows if/when an item reaches the output. The hopper in the middle position and the hopper or dropper at the right each contain a stack of items. The structure block all the way at the right can be used to reset all of the stations.
2. Press the button at each station A-E, and flip the lever to turn on station F.

Expected results

An item reaches the output hopper at each station.

Observed results