When blocks are being updated/moved by a piston(s), the texture glitches out and makes the game run slower than usually. Occasionally this also makes it worse for any piston elevators I use, where if a player is on top of a piston or block thats being moved upwards, that player glitches through the bottom or to the side. Even more buggy is when a player tries launching themselves up with the help of a piston + slime block, they just fall of to the side instead of launching up.