The video cuts away right when the second engine shuts down and the fire starts. I really want to know the cause of the fire. Maybe the fuel side preburner valve didn’t close and fuel was leaking all the way through the engine. However, the fire looked too high up on the airframe to be from a leaky engine valve.

Edit: after another look it seems like the fire is from the engine and the wind is blowing it up the side of the airframe.

(and then exploded a few minutes later?)