@Phaedrux
checked general settings "Duet Web Control 3.1.1"
Just for the heck of it I wrapped the flat cable in aluminium foil about 6 layers or so and then covered that with some captan tape to avoid disaster then a bulldog clip to clamp the foiled cable to the frame . Measured about 24 ohms from connector end to frame for a shield 22cm long. No change in file behaviour
I can live with the way it is for now . It was nice though to be able to use the card 1, I preferred leaving the system SD card 0 alone as much as possible