Thanks Nick – well, that clears up the H9 control software mystery!
It seems unlikely that this is a bad socket, as this occurs on all 4 stompboxes. It doesn’t seem to be a ‘cable waggle’ issue; could it be that the original moulded jack is wired wrong, or badly??
I’m reasonably handy with a soldering iron, so a next cheap step might be to refit the expression pedal with a new stereo (TRS) jack…
PS, whilst you’re on…I’m intrigued – it it possible to control more than one stombox at a time with the H9 controller software, with a single USB cable, by connecting subsequent stomboxes to each other with midi cables?