Right off the top of my head, in 2 minutes I came up with 4 widely different scenarios that equally fit the known facts at this moment. Based on previous events with a similar profile - extreme dive from cruise altitude.
And I've probably missed a couple - aviation is pretty good at coming up with "new" holes in the cheese,, that we've never run across before.
I don't list them, because someone is sure to start "fixating" on one or the other - with 80%+ odds of being wrong. Which is a poor way to maintain credibility.
I expect additional information will be forthcoming, which will eliminate some of those scenarios, and point more strongly to others.