This is probably nothing, but since lots of posts are equating a loss of upstream fuel pressure (upstream of the HP fuel pumps in the engine) with a blockage in the fuel line (causing cavitation), it's as well to realise that it's not just a blockage that can result in low fuel pressure from the LP pumps (in the wing tanks).
A few years ago we were completing maintenance on a Fokker 100 and for some reason the LP fuel pump delivery pressure on the pumps in the LH wing were only delivering about 50% of what they should. To troubleshoot, the pumps on the LHS & RHS were swapped - the problem STILL only occurred on the LHS. That eliminated pumps as the problem, and we started to look for a blockage in the lines downstream of the pump as the only explanation. No joy.
During the maintenance input, the LH engine had been changed. This required swapping the IDG (integrated drive generator) from the old to the new engine. During that procedure, human error had misconnected the three phase wiring and earth so that the AC three phase output from the LH engine generator was wrong.
Lesson No 1 - no other system on the aircraft was bothered by this except the LH fuel pumps. Lesson No 2, although the Ground Power Generator Control Units monitor the phase quality of the power coming to the aircraft, ordinary Generator Control Units do not (on that aircraft anyway). So there was no fault announced at the front of the aircraft.
Now in no way am I suggesting that on this 777 the generators magically re-connected themselves in flight. However sudden low pressure from all LH & RH pumps could (in theory) occur if the phase relationship of the power supply to all of the pumps suddenly changed.
Also, if the 777 is anything like the Fokker 100, it might only be the fuel pumps that would have a problem with this. How that might happen in practice I don't know - I would think it so unlikely as to be almost impossible. Also, even if it did happen, I would be surprised if such a loss of pressure starved the engines - but perhaps in combination with other things it is (theoretically) possible.