I doubt most failures occur when the amp is connected to a load that's within its limits. I don't remember hearing or seeing that ClassD do as well with extremely reactive loads and extremely low impedance. Heat.... lots and lots of small components close together, with limited or no heatsinking... major bits are heatsunk - but the way these modules are set up, most FLIR pictures show hot patches.... on typical AB designs all the "hot bits" get heatsinking...
