Secondly, could strong updrafts be a major factor, up to and including the final descent and crash? As I understand it, aircraft stalls are a function of angle of attack, and pitot tubes don't function well at high AoA values. A 50kt updraft at a speed of 447 kts (mach 0.78 at fl350) would add about 6.4 degrees to the angle of attack.
I don't think so. If you fly, on autopilot holding a constant pressure altitude, into an updraught, the AP pitches the aircraft
down, to maintain the pressure altitude. Your airspeed increases - possibly a lot.
Thirdly, what woud the autopilot have done in a strong updraft before disconnecting?
It will pitch the nose down, and the airspeed will increase rapidly.
Whether the AP will disconnect just because of the updraught, I have no idea but I doubt it.