I was testing an automatic piglin trader in creative and some of the droppers did not fire, even though they had power and items. On the F3 menu the ones that were fired always said "triggered: false" while the broken ones always said "triggered: true." If I broke and replaced the redstone, or placed blocks around it, it will work once and then go back to not working. I tried putting a trapdoor next to it that would activate to update the block if there was something like that but it did not work. On the first picture you can see the 3 piglins that do not have gold, and the 2nd shows the redstone setup.
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Panda4994
Thank you for your report!
The bug you described is a combination of two tracked issues. I liked this issue to them, but the gist of it is that droppers can get powered from further up than you would expect (MC-108) and then they don't always get updated correctly because the order in which the wire updates is random (MC-11193).
To fix your build, try using upside down slabs (or glass or another non-conductive block) below the redstone.