The Fuel system worked fine
It sustained damage from Cavitation, but even with that was "able to function normally". The squishiest suspect is of course, Fuel.
1. Ten degrees "off spec.". Not "better than"; OFF SPEC.
2. Fuel contained some amount of water, deemed "less" than "excessive."
3. Water and Jet don't "mix" (non-soluble)
4. Tank Temp., at -34C would freeze water immediately
5. Boeing Captain Carbaugh posits "Ice Crystals", a "Temperature issue"
6. The Heat exchanger has yet to be exonerated from involvement.
7. Fuel and Water could have transited the LP pumps
Possible: Given a seriously cold-soaked engine Pylon and barely warm heat exchanger, ice crystals could accumulate in the exchange matrix of the exchanger, blocking flow to HP pumps.
For this to have happened, the timing sequence of engine thrust loss needs to be seriously considered to satisfy many possibilities.
1. The Fuel/Ice "mix" would have to be inordinately homogeneous between the two main tanks.
2. If the ice crystals had already been formed, further "freeze" may not have been possible anyway.
3. The Fuel/Ice emulsion, at flight idle, transits the Fuel works fine, no loss of supply or even thrust.
4. At Throttle up, the Fuel is moving more rapidly, ice is "collecting"
in restricted spaces, but the engines respond fully before the accumulation can get ahead of the supply.
5. At full flow, the ice crystals gather rapidly in the exchanger and elsewhere, constricting the Flow of Fuel. #2 drops power.
6. Drawn from Port Tank, the Fuel ice "emulsion" is perhaps 1.5C warmer than the Starboard Tank, and #1 drops 8 seconds later. (Port Tank is in sunlight throughout the flight, the inner portion of the Starboard Tank is in the shadow of the Fuselage.)
Why Crystals and not surface accretion? Agitation, and lack of nucleation. Any "Slurry" will shed its solids at turns and pressure foci differentials. It has to be Fuel Fault.
Airfoil