Here are a couple of photos showing how the black rubber disc (hockey puck) should be installed:
I believe that your hockey puck has become dislodged from the metal plunger that is pneumatically actuated to push the hockey puck straight up from the floor to press on the bottom (underside) of the sliding pocket door.
That happened to me. It's a simple fix. Just fish out the hockey puck and clean one side of it and the top of the metal plunger (isopropyl alcohol works well) and apply an adhesive (I used E6000 adhesive - https://www.amazon.com/E6000-237032-.../dp/B004BPHQWU
). There's not much room under the door to get the hockey puck placed back on top of the metal plunger, but, enough room to do it without too much difficulty.