Originally Posted by
FluidFlow
Hence it is the handling of the variations in air properties that I believe may be an issue and may have caused HAL to give up.
No, the Auto thrust and Auto Pilot disengaged because the speed measurements disagreed, which is most likely due to uneven blockage of pitot tubes and their drains due to ice.
Air properties and computations will be a common-mode problem, but are of considerable interest in understanding the state of the A/C when handed back to the pilots for manual control.