I've recently answered to a similar thread describing this problem in 1.15.2 (showed below), but since it affects also the latest forge version I think it deserves his own post (sorry if I shouldn't have, I'm new to the forum).

 

 

Replicated in forge-1.16.1-32.0.24 (latest) with no mods installed in a new 1.16.1 minecraft world. This bug does not occour in vanilla 1.16.1

 

Bug description:

(I'll just quote what RescueGum wrote in the 1.15.2 post, since the bug works in the exact same way)

 

Quote

when items are pulled from doublechests with a hopper/hopperminecart, comparators going 'out' of this double chest do not update properly, until the doublechest is opened (and thus itself block-updated) by the player manually.

i noticed that basically only the 3 comparators going out of the corresponding half (*) of the doublechest from which the last item was pulled update correctly and the 3 comparators on the other side no not update. it does not matter from which side of the doublechest the items got pulled by a hopper, only in which half the last item was located inside the chest.

(* standing in front of a doublechest, the 'left halft'/'left block' of the inventory corresponts to the top 3 inventory rows of this chest, and the 'right half' of the chest to the bottom 3 inventory rows)

I add that the comparators affected by this problem update also if you right click on them, similar to how they behave when you open the doublchest as described in the quote.

 

Thanks for your attention, hoping this bug to be addressed soon (I've noticed it's pretty old).

 

Have a nice day.

I confirm that this issue exists on 1.16.1 and 1.15.2 latest forge versions as of writing this post, using hopper insertion. Filed a bug report (MinecraftForge#6873)