If you have a line of dropper/dropper combos (two droppers facing into each other) with one item inside every dropper/dropper combo, and power all of the droppers on one side of the line, there will be a few ones that don't transfer the item into it's pair. This might be the same bug as [MC-10174]
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I think I see the problem, the redstone current doesn't have "velocity", it is an instant travel, so they all go off simultaneously. This can cause inconsistencies, until it's fixed (if it is) your best bet would be to press that button several times or have a brief delay between each transfer, which I don't know how to do when they are right next to each other...

Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.