The issue is happening after there's a pulse from the right switching the redstone block over starting a hopper clock and pushing the closest piston down for one tick causing the block to stay down. Once this clock is done the redstone block is moved back activating the repeater and triggering the observer to power the piston for another tick, (should be pulling the block back up.) instead the piston is firing twice and leaving the block down. I've replaced the piston with glass and the observer is only showing one firing of one tick. Happens in single and multiplayer.
This works in 1.13.2