Weird, I noticed when I got home on the ebike that instead of stopping the sportscam recording I had started it. Definitely remembered starting it when I put in on the ebike in the bike shed at work. Assumed that out of habit I had started it as I set off and had actually stopped it
Played the recording back and it runs for around two thirds of the ride and stops no where near the max length of a recorded video. The battery is fine and SD card virtually empty. Reformatted the card as I cannot think what else beyond the sportscam going faulty could be the cause.