Footswitch decided to stop working on Saturday night. The D pin connector on the SD1 has been a bit wobbly for a long time so I suspect a bad connection there.
The actual footswitch is OK because it works on my Audya.

I opened the SD1 and gave the D pin connector a wiggle but I can't really see much looking from the top. Looks like I would need to disconnect all the ribbon cables and unscrew the PC board to get a proper look.

Can anyone help or advise on this one ?

If it helps anyone else I have found the problem. Looks like a very common one or at least very easy to happen to you.
I opened the SD1 and removed the circuit board to find that one of the legs on the D pin connector had a bad soldered connection on the underside of the board.
No doubt this is caused simply by connecting and disconnecting the footpedal time and time again. It is quite flimsy.