Speculations by a real pilot - entering severe weather could / will destroy any aircraft regardless of design / cost. A severe turbulence, hail, icing, lightning strikes and heavy precipitation could destroy cockpit glass, freeze flight control, knock out avionics, shutdown engine or cause catastrophic air-frame failure. If you look at ATC traffic, civilian airlines were turning around, but it appears this pilot decided to "punch through" the weather. (I'm guessing since no flight path was released to the public). Decision making process to proceed into shit-weather would probably be the root-cause of this.
It took days to find missing F22 back in 2010. https://www.jber.jb.mil/News/News-Articles/Article/291404/missing-f-22-pilot-update/
https://en.wikipedia.org/wiki/1989_Belgium_MiG-23_crash
I wonder who hacked this Mig-23?
https://www.bbc.com/news/uk-66798508
here ya go.
Booze is expensive at an airport.