When placing an observer next to a chest (as in the first attachment), it will be updated by opening or closing the chest.
When placing an observer next to a block underneath a chest (as in the second attachment), it will be updated only by closing the chest.
This bug does not appear to affect shulker boxes, but does affect trapped chests.
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Comments 3
I think this is another problem entirely - the problem isn't being caused by the piston not updating to the observer's signal. There doesn't seem to be any signal at all. Note the name and steps of the linked bug - "powered through blocks", which you can clearly see in the screenshots is not the case; rather, the observer is watching the chest through a block, thus the problem is happening at the observing end rather than the output end.
Works fine if the chest is next to the observer.
Most likely caused by MC-108696.