Yep - that is all set ok, Not changed, and checked it.
The last time it happened, I had absolutely no track log - had gone completely.
This time, I just dug in the Archive folder on the device by hand (using file explorer) - and there was a log with the right date. So it looks like the "daily save" worked.
I wonder if last time, I switched off straight after the ride, and then didn't power on again before connecting by USB to my computer. Maybe that stuffs up and doesn't save the last active log. I imagine the "auto save" happens when you power up and it notices the date has changed, so perhaps that is where the software glitch happens.