Parameters not saving after reboot

I am not sure if I have a problem with my FC. It’s a PixHack V5. I have multiple V5s and the others work fine. This one does not store parameter changes. It loses frame_class and every time I set brd_safetenable to 0 after reboot it resets to 1.

Is this a hardware problem or am I doing something which I may have forgotten over the long winter?

I am running the latest ArduCopter version 3.6.7. I have also tried 3.7