From AAIB report:
No individual parameter from the flight of G‑YMMM
has been identified to be outside previous operating
experience. The analysis is concentrating on identifying
abnormal combinations of parameters
The really interesting thing here is: how often has something similar to what happened to MMM occurred (restricted fuel flow) but gone unnoticed as the restriction was not severe enough to cause engine problems? Could it be that what the industry regards as 'safe' flight profiles are sometimes 'outside the envelope'? We know from this accident that there is little/no evidence left behind, so shouldn't expect too much from records of other flights.
This may not be a specific RR/Boeing problem and could possibly apply to large variety of turbine aircraft that are operated in a certain way...