Chevrolet Volt Propulsion Power Reduced: Saturday 27th July, Propulsion Power Reduced

Today's trip is where things get a little bit more interesting.
First the really boring bit. After the overnight charge I had a 43 mile range estimate. Drive 4 miles to shops, fully recharge while shopping, drive home and recharge again. Range now says 44 miles.

Drive 24 miles to Oxford M40 services, partial charge of 2.21kWh bumps the remaining range back up to an estimated 32 miles remaining:

Arrive Aylesbury at 13:23, 21 miles range remaining:

Leaving Aylesbury at 15:22, the range estimate has gone up by 1 mile but that's not unusual.

At 10861 miles the range estimate was reading 2 miles, and I was on the A40 near Wheatley doing about 50mph. This road is not in a mountainous region.
Within the space of about 3 seconds the range went from 2 miles to petrol engine and propulsion power reduced mode with the engine desperately trying to make up the charge. I pulled over as soon as there was a suitable side road and took this picture:

That isn't normal behaviour for a Volt. I wasn't accelerating, I wasn't driving up a hill, I was reaching the end of the available charge, but 12.9kWh is about right for 10.8kWh (which is about what I get on a normal day) plus 2.21kWh top-up (less a little charging loss). This is actually new behaviour I haven't observed before: previous PPR incidents have all been when I return to the car having parked with lowish range estimate.

At this point, since I'd stopped for the photo, I turned the car off and on again and PPR cleared so I was back to normal acceleration.

16:43, arrived in Faringdon and parked. There was a hill nearby, but we parked at the foot of the hill and walked up.