Sticky joystick

Just put together a Picade console with a Player X to act as a second joystick. Simple to get up and running, but the joystick is a bit sticky on the left/right, it feels more like an old X-Arcade joystick on that axis (i.e. horrible). I’ve checked that nothing is interfering with the movement underneath. Is there anything I should do to fix it or is it a bad joystick? Many thanks for any advice!

Edit: I removed the bottom plastic cover and the microswitches and the problem seems to be with the metal washer that sits flush in the plastic housing on the underside of the joystick. It is moving and getting stuck. Is it supposed to be glued in place?