Teal,
Beyond my technical ability to respond. Planes have been flying into, and out of, China for decades.
To say it could been this, or could have been that, is pointless IMO.
It could have been a zillion things.
No one's brought up the chance that it could have been two expert rifle shots at the same time to both hit the fuel control units in the exact same spot.
No one's brought the chance that it could have been a meteor that broke up in space and two small pieces hit the engines in the exact same spot.
Patience. They're working on it.