It has been discussed before - Pitot tubes have a drain hole, to allow ingress of liquid to drain, their calibration assumes the leak. If the drain hole blocked they will over-read, not sure what percentage. If the pitot inlet then blocked you can imagine this high reading being locked in - until the heaters melt the trapped ice in the drain and speed reading drops to zero. If the a/c flies into a fine ice cloud, all sensors could be affected in a common-mode fault. If the auto-thrust reacts to the over-read before rejecting the readings - the pilots could be handed back control with insufficient thrust to maintain current true airspeed.
The drain holes are designed to cope with ingress of low altitude rain/hail storms, and their detail design will differentiate different manufacturers models.
I assume regular maintenance procedures do non-abrasively clean these drain holes - dimensions critical, but why do problems appear to have started to occur years into operation? Of course there's also climate change...