after investigating, i discovered the cable had a problem at one plug end. i chopped off about half a foot of cable and re-attached the plug. now everything's fine.
still, i had never come across a cable that would partially short out. i played the whole gig through that cable without static, hum, pops, noise, etc. just an extreme loss of gain.

so, to future generations, know that cables can
partially fail (partially being different from intermittently). later, ron