I built this to test after encountering this problem on my server. The barrel works as expected initially, but once I quit and reload the world it no longer sends items into inventories below when the redstone signal is off.

I tested some more and found that the issue also applies to barrels when placed in a situation which would lock them (if you place the barrel in the image last it will become permanently locked)

Thank you for the bug report!

I was looking at the logic for redstone levels, why are hopping barrels being skipped here? Not sure if its the cause of the issue or just something I'm not understanding

Sorry for not answering in so long; guess I better do so for the benefit of future lurkers as well.

The reason is that the output level concerns the redstone output of the Barrel, and with Hopping Barrels being able to take redstone input, that'd make a mess of things.