Vello wrote:

They start from the same point, in Russian media poor fuel is one
discussed thing.

The obvious problem with that idea is that poor fuel would usually
just stop the engines, leaving them 30,000 feet or so of gliding
descent in which to report their difficulties and attempt power-off
landings.

It seems rather likely that some form of malice was at work and that
the technical investigations will merely discover whether hijacking
or bombs or some other form of sabotage was used.