sounds like something was interfering with combustion. Possibly high velocity air/ air turbulence interfering with the air/fuel stoichiometry within the combustion chamber? uncombusted fuel would be my initial guess.
I was the project historian for the National Aerospace Plane from 1988-1995, and finally got the history published as “The Quest for the Orbital Jet,” around 2000, from the USAF. It may be limited release, but it should be available somehow. Anyway, this project shows how far we were from the goal of attaining orbital velocity with a jet.