Airbus Systems have all been well tested with multiple redundancies built in. Something else happened that made both automatic and manual control impossible.
Much speculation concerns the ACARS messages - but if there was a catastrophic failure some of the more informative fault reports may not have gotten through to the COM link or they may have been queued for transmission but never made it. We shouldn't assume that the faults transmitted were the principal faults that occurred. For instance if another unreported fault disrupted power to the pitot heating, then the latter problem would be a symptom and not a cause.
Could solar weather conditions have been a contibuting factor, possibly triggering single event efects (SEE) and/or a solar proton event (SPE)?
Source:
SolarSoft Latest Events
There was an increase in X-ray activity from the Sun (ref. GEOS 10 in upper graph), starting late May 31st which continued through June 1st and in the same time frame the coronal hole graph show a pronounced dip at the approximate time the aircraft went missing (Kyoto Det/PFSS in lower graph). The accident site is also slightly north of the South Atlantic Anomaly, an area of radiation in the form of trapped protons where the lower Van Allen belt reaches down into the atmosphere. The X-rays preceded a solar flare which occurred approx. 12 hrs after the aircraft went missing.