takata
"Triple probe fail". This is not necessary at all to generate the ACARS msg ADR disagree. Two bad and different speed values are enough, because the system can't decide which of the three values is correct.
A sobering example from my own safety research field. We had a near catastrophic event in the Forsmark nuclear power station a couple of years ago when two out of four almost identical parallell safey systems failed at the same time (always assumed impossible). The two failing ones together managed to shut down the instrumentation in the control room. The two surviving ones kept the reactor going. These systems had higher safety requirement rating than most things on any aircraft.
I can even imagine some kind of mechanical fault in the rack containing the ADIRU:s from the inertial forces when going through bad weather causing bad and erratic signals. Even some loose object may have hit them. Both of these possibilities have been subject to safety directives, although for other aircraft types.