I've added a simpler test setup. To do the test setup, place one double chest, and below it, place 2 single chests with a hopper pointing into each single chest. Reload the area to place (done so by teleporting far away) and place 3 items in the chest. Note which chest has 2 items in it. Take the items out of the chest and break the hoppers. Place the one hopper pointing into the chest that had one item, and then place a second hopper pointing into the chest that had 2 items in that order. This sets hopper update order because last hopper places gets added to tile entity list last. Place 3 items in the chest and notice which chest has 2 items in it. Take the items out, and reload the area again. Place 3 items in the top chest and notice how the other chest has 3 items in it.
Do note that this behavior is locational, and is not directly related to dust locationality.
Still a problem in 1.16.5 and 21w08b, and also applies if you unload the chunks via moving away. This bug is also known to some people as "hopper aging"
Still in 1.16.5 and 21w06a
Can confirm POI data mismatch crash in 20w49. Although I got this crash from activating a redstone contraption that uses pistons and composters in it
Still in 1.16 pre6
Still in 20w22a
Still in 20w18a
Still in 20w17a
Still in 20w16a
Still in 20w16a
Still in 20w16a
Still in 20w16a
Still in 20w16a
This is not the case, redstone does not prefer going upwards and is working as intended. What is happening is that the redstone line going upwards is shorter because the redstone dust is powering the solid block due to 1.16 dust behavior. Replacing the dust not on a block with a target block makes the setup RNG as expected.