Captain Mongo
LAV SMOKE was third message sent, this leads me to believe whatever brought the AC down did not originate in the Lavatory. If a fire originated in the lav, the attendants would have been trained to aggressively fight the fire once made aware of it
Exactly why I posted
Above The Clouds
Just bear in mind that because you receive a "Lavatory Smoke Message" and an "Avionics Smoke Message" doesn't mean a fire started in either of these places.