Green Dot:
I repeat my theory here, since you mention the suction bypass system. Boeing acknowledge that gas or air can be trapped in the suction line and cause flame out or thrust reduction under suction conditions.. If some unusual circumstance ( excess gas in the fuel trapped under pressure in the line or LP pump icing reducing manifold pressure) caused the suction line NRVs to open, enough gas could be introduced, almost simultaneously, into both sides of the fuel supply manifold and starve both engines of fuel. There would be no evidence of that after the event.