This bug also existed back in 1.17 but hasn been fixed since
MCPE-172953
Droppers update order can change after restarting your world
Open
1
(Unassigned)
1087352
Confirmed
Multiple
1.20.20.21 Preview, 1.20.20.20 Preview, 1.20.10, 1.20.11 Hotfix, 1.20.40
Retrieved
Droppers and dispensers have never had a defined update order in Bedrock Edition. However, they sometimes seem to because their update order is not randomized on every tick, unlike piston and hopper updates (MCPE-16371, MCPE-28890). This confuses players as shown by the reports linked to this ticket as “relates to”.