As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED: LAVATORY SMOKE WARNING CAME ON AT CRUISE ALTITUDE FOR ABOUT 3 SECONDS THEN WENT OUT. FLIGHT ATTENDANT COULD NOT CONFIRM ANY SMOKE OR VAPING. MAINTENANCE PERFORMED LAVATORY SMOKE DETECTION WARNING SYSTEM TEST PER AMM 26-17-00 WITH NO LIGHT OR WARNING INDICATED.