I'd checked the weather report the previous morning and expected it to be a cold, frosty morning. In the morning I then walked the two to three miles to this spot with the Cambo - with the aim of getting the low sun raking across the fields.
@Andrew O'Neill - yes, it's become apparent that my Epson V850 is not a happy scanner. I've spent some of this evening trying to understand what may have caused this and have a few things to try out.