Has it occurred to you of the possibility that somethings had to be flushed away , if the system was somewhat acting up or affected the area ? Good thing the crew is able to prevent nasties like the flight stinking up or worse
Perhaps you should just email them your flight number & get to the bottom of it , pun unintended !
Think one of the A380s that I was on this year had lavatory problems too , happened during the flight
Don't think it was on same flight as OP , mine was in June . They did not manage to resolve the problem so it remained locked

Use the feedback forms next time , request for them inflight or at SKLs .