I'm in version 1.14.4pre-6 and have average redstone skills, so this is my player conveyor belt design, and this piston won't turn on. It works when I update it, but I don't see why I have to with this design
It's not completely clear from the screenshots, but you might be blocking the pistons at first (with an extended piston, a tile entity, more than 12 blocks, obsidian or whatever) and then unblocking them after powering them. Pistons only extend when unblocked if you remove the block directly in front of them, otherwise they don't get a block update. The workaround would be to power them later.