Thanks for the idea. Since my post, the problem got worse, all channels lit up, no control.
This is a newer Cat5 cable (6 monthes or so), not the original one I had. I didn't try a different cable yet, however...
On the amp Cat 5 insert of the amp, I did see something awry (see pic). One prong was lower than the others, and a few weren't sliding freely in the slots. I attempted to adjust the prongs with a tiny screwdriver. Same problem initially, but after reattaching the cable several times, the pedal works again. I think it's likely to reappear though.
Wondering if the female end on the amp could be replaced easily? Not sure if you're able to answer that...
Either way, thanks for the help.