DPU control depends on continuous perfect communication with zero loss of signals and circuit reliability. Anyone who watches over-the-air TV or uses a computer knows this is never perfect. I remember a photo showing six semi-circular pockets where the rails had melted down to the foot because the DPU didn't get the message to get out of Run-8 when the train stopped. The wheels still turned at max power with the DPU stopped and melting the rails. Not saying a DPU communication failure happened here, but it probably is one of the first places that will be looked at.