Icing
I seem to recall an article in RCJI concerning many unexplained flameouts at a jet rally held in cold weather. (Winter Jets in the U.K.?) If I recall the only explanation for the flameouts on normally flawless running engines was icing. The trouble was that the evidence melted by the time the model was retieved due to residual heat from the turbine. Maybe we'll never know!?!
Kevin