This morning CNN stated it was Lithium Batteries that was aboard on the plane and that may have caused an electronic shut down.
A fire on board would cause any responsible pilot to make for any nearby airport and they would be radioing Mayday.
They darn sure wouldn’t fly another four hours and turn off all communications during an emergency.
Most of the theories on this thread fail to take into account a complete lack of any attempt by passengers to communicate a problem with the aircraft!