The bottom piston does not extend, and I am not sure of the issue, it worked back in versions 1.19 and previous, and I am not sure about 1.20. It does not need a block update (unless there is a block update bug, of course), as both the top piston and the redstone dust powering it (redstone dust can give block updates if it is 2 blocks away when it is powered) in theory should give it a block update

World Zip File: https://drive.google.com/file/d/1aRuZx7C9Ub-a-4ydHzR5hg9mE5BAPzsF/view?usp=sharing