This bug has also happened to me, but I was standing literally right next to the comparator
Comparator did not update. Still outputting a signal of 1.
Added more to the hopper inventory. Comparator should output a stronger signal.
Initial hopper inventory.
Initial hopper inventory.
Initial shot.
Here is the working we are currently using in our server. Create a block above the problem comparator(s) then run redstone on top of that block...turn the redstone on/off to cause an update. This is currently being used in an autosorter for a quarry...the items are transfered by cart to a sorting system and the cart runs over a detector rail which briefly turns on a line of redstone that runs above the rows of comparators.