This is quite a bit oversimplified, but with Airbus, until you degrade fully to direct law, the computer is still trying to fly the aircraft as it sees fit, up to and including
overriding the aircrew's input. All that "Autopilot" really means is that the aircraft is holding heading and altitude in accordance with its instructions, but the computer is still flying the aircraft.
Once the computer accepts bad data as gospel, it can start doing stupid things with the aircraft. All it needs is a trigger for all heck to break loose.
The computer gets its data primarily by accepting the middle (median) value of the 3 input channels for key flight information.. When some situation occurs that affects 2 or 3 of these data inputs channels in some common (but bogus) manner is when Airbus gets confused.
ACARS information from the flight indicates that all the Airspeed information channels were considered bogus at some point.
Sheer speculation below but possible initiators for loss of control are:
1. The Aircrew being confused by erroneous airspeed indications and stalling the aircraft in Alt (2) law.
2. The aircraft being confused in Normal Law, and applying the wrong dynamic laws for the aircraft and thus dynamically diverging from controlled flight.(Think servo system that is stable but too much gain.)
3. The aircraft being confused in Normal Law, and applying Mmo/Vmo protections inappropriately, then degrading to Alternate law and stalling.
4. Something even stranger that I haven't considered
.