FYI. This is still an issue in Java Edition 1.16.5
I've been having this issue in 1.16.5. Just started hosting a server and have been getting reports from the players that there's a bunch of spots where they can't place a block. I've been having them tell me the coordinates for those blocks and then I just use the setblock command to place air in that spot. This fixes the issue, but it's been so frequent that I spend most of my time just running the setblock commands. Is there an actual fix that stops this from happening? In the picture, I've put red glass directly above the spots where you can't place blocks.
The comparator detects that there's no items after I took the charcoal out. It took me about 5-6 builds of this build to replicate the issue so it's not super frequent, but I figured I should report it anyway. The dropper is supposed to "drop" the item once the comparator detects something is in it, but when this happens, it won't "drop" even if I right click the comparator to force a pulse from the observer. The fix for this (that I found anyway), is to break the hopper above the bugged dropper and replace the hopper and redstone (same orientation); don't know why it is, but I broke and replaced each piece and replacing that hopper seems to be the thing that fixes it.
Maybe my issue is different from the OP, but in case it isn't, this could be related to MC-130961