I suggest that could be the Crew Oxygen Bottle. Most Airliners have this vulnerability. It would cause massive electrical issues, decompression, and now from the latest report the autopilot is OFF, the aircraft was left meandering. It’s really not that difficult if you know how the avionics bay is constructed and how a disabled B777 once trimmed for cruise could fly on to fuel exhaustion.
Having just read the report, it pretty much says the opposite, that there are no realistic (or likely) failure modes that would leave the aircraft flying in straight lines then making turns then flying in straight lines, etc. without pilot intervention of some kind. Same with altitudes.
There are so many incredibly improbable things that had to happen one after the other to make the aircraft follow the reported path on its own, that this can effectively be discounted. Alien abduction is probably orders of magnitude more likely.
We are not talking about an event that caused a hull loss shortly after otherwise things like oxygen, batteries on fire, decompression, etc. would be high on the list. We have an aircraft that flies on for 7hrs in a way that experts tell us requires a (live) human on the flight deck, at least for the first couple of hours.
If we want to talk Ockham’s Razor, then the simplest explanation is this was all deliberate action by at least one person (which they imply in the report). No repeated super-unlikely happenings required. Not the first time for something like this, either...