There was a very good "air crash investigations/seconds from disaster (or similar)" on what happened and how the only logical option left was ice.
If I remember correctly, and perhaps someone with more knowledge could correct where im wrong, the heat exchangers tubes where the fuel would run through protruded out of the cylindrical container only by a couple of CM (if that) and due to the fact that the oil only really heats the parts of the tubes that it touches or that are in close proximity through conduction, passing almost waxed fuel through at -40 degrees C or or close, the protruding parts of the tube that stuck out one end, were not heated enough, and therefore when the FO disengaged the Auto Throttles, and added power, a flow of frozen fuel rushed through towards the tips of these pipes and physically blocked them, starving the engines of fuel..and well we all know what happened next.
I believe the fix was fairly straight forward, as they shortened the pipes so that nothing protrude and so that it was all properly heated.
It was a 777-200 ER G-YMMM which I thought had RR Trent 800 as opposed to the 300 ER which has the wonderful GE90 Powerplant
Sorry I cant find a link to the investigation, but I would recomend you look it up as its very interesting to see the mock up of the system they recreate