Now that a factual report has been released, we can at least focus on it.
I find the following timing sequence of particular interest.
UTC
1701:43 a/c at 34998ft
1706:43 a/c at 35004ft
1707:56 with over 12 minutes to run to IGARI, crew report level at 350 without previous ATC instruction to report reaching or when level.
1708:02 ATC response instructing to maintain level.
Report at 17:07:56 : Could this have been a deliberate action by whoever was going to change the plane's flightpath to confirm to ATC that all was well, immediately prior to the ensuing diversion ?