Picture or video would probably help but best guess is you cut off the redstone signal some how. His newest design using all observer blocks is nearly fool proof though if you are in a version with observers.
Also if your in bedrock power budding for pistons doesn't work and they need to be powered more directly. Merely powering a block diagonally to the piston does not work.
I’m on Xbox, however I’ve tried the design on pc and switch versions. The design I’m using is the super compact with 6 pistons topped with 6 pieces of red stone and two repeaters set to two ticks.(not sure how to post a photo)
Yeah that door only powers the top most pistons, it relies on bud powering to do the rest. I am not sure that would work in bedrock version, which if you came from Xbox is what your playing. I am fairly sure even if you play on PC your using the Windows 10 version of the game and not java, thus again you don't have that "glitch" feature to work with.
I think all you would have to do to solve the problem is continue the redstone signal from the top down and power the bottom pistons. It might not be quit as smooth however and I don't know if the timing of the pistons firing would be off or not.