The weather was said to be good for the flight but at 35,000' was it possible the Jetstream was causing severe turbulence on the flight?
I cannot find a historic Jetstream map, but by reversing the time using the following link to 0.00 hours and assuming the trend continued since the early hours of March 8th then there appears the Jetstream was strong at the time.
Weather Model - Asia Jet Stream Wind and 250 mb Pressure (STORMSURF)
Maybe there was severe turbulence early into the flight once it reached its cruising altitude which seems to correspond to the strongest part of the jetstream (if I am reading this right)
Apologies if I am way off, but I at least have read this entire thread before dipping my toe in.