Wx deviations ?
Precise calculations using the last ACARS position message coordinates (as reported by BEA) show that the crosstrack error (XTK) was 2.95 nm left of UN873 centerline.
Examination of the messages reception times and precedence, assuming equal transmission times, exclude the possibility that the a/c was on track and on course when the AP disconnected.
This can neither be explained by assuming they were using a tactical route offset since these offsets are only allowed right of track.
Hence, I tend to believe there is a strong clue that weather deviations had been in progress when the first cockpit alarms occured.