I believe that if it is known ahead of time that a lavatory is non-functional or will be blocked off by the crew then passengers should be told before boarding and given a choice of switching to another flight, regardless of cabin (as a locked out lav can affect whole plane, directly or indirectly).

As regards compensation, a bit harder in Y but for J I would think that if one pays thousands of dollars for Polaris , it should be grounds for compensation if a lav is locked through the flight, as part of what one pays for, and expects, in J is a higher lav to pax ratio.