Hey! To my knowledge, redstone use is very limited across the network intentionally to prevent lag on the gamemodes. Whether slime blocks/double piston extenders are meant to be included here, I’m not 100% sure.
I can appreciate the frustration with this, but at the same time - it’s better to sacrifice use of some redstone, than to have 90 players on one server using all sorts of redstone contraptions, and the server becoming almost unplayable or having huge spikes in lag when someone opens a redstone door!