Just to be clear, the .02 shutdown rate is for 180 minute ETOPS - longer ETOPS have correspondingly better shutdown rate requirements. However 180 is important because as I mentioned earlier 180 ETOPS will get you anywhere in the world (although may require less than optimal routing).
No first hand knowledge here but I suspect Kelvin is right and this is the same issue that ANA had. As I understood it - the ANA issue was related to corrosion of the turbine blade. At the high temperatures that turbines operate at, many materials corrode that don't corrode at lower temps - and some of the contaminates and impurities in the air and fuel act as catalysts at high temperatures.
The engine companies try to prevent this with various coatings - I suspect whatever coatings Rolls is using on the Trent 1000 are not working as well as they'd planned...