Dropper sometimes don't drop out items when powered. -> Droppers triggered by observers column noticing water change from bubbles to normal water can be set into BUD state and desync between client and server. To reproduce build like in screenshot, break soulsand, then replace it. The lowest dropper won't trigger despite being powered.

video: https://www.youtube.com/watch?v=pokH-HYgRmE

After a bit of investigation:

after removing soulsand, the lowest dropper desyncs between client and server. On client it looks in F3 as triggered: false, but on serverside it stays as triggered: true. It synces up when opening it's inventory. So pretty much removing soulsand sets lowest dropper in powered BUD mode. Placing anything next to lowest dropper resets it to unpowered mode.