"Which would indicate a stall and probable spin entry."
FWIW thats the best sense I can make of the reports so far.
"So back to my point about the cause rather than the visible symptom?"
Cold day, lots of cabin heat, cracked exhaust, carbon monoxide poisoning of the PIC is a leading potential scenario. Wouldn't be the first time. Sadly, won't be the last. It doesn't happen often, but does happen.
Small electronic CO2 detectors with audible alarm are available - can go back in the flight-bag or be left in the aircraft after flight.
Is the CO2 risk worth some outlay on a detector? Like having a liferaft after leaving a ditched aircraft - if it happens to you - there is no question - it is worth it. I am not sure there is a better way of mitigating this risk.