2008 Hollowbody II (core, not SE) question. Issue when using two output configuration (mag pickups to amp, piezo to PA)

[mhurt2000]

When I use a single cable in the Mag/Mix output to my amp, the guitar seems to work fine. Piezo signal can be blended or used as main out based on microswitch setting, mag output is fine when switched to mag only, etc. However, when I try to use the dual output feature, things go sideways. There is a strong signal in both channels, but neither the mag or piezo volume pots seem to do anything to modulate the signal level. In fact, for the piezo output, the lowest level setting for the volume pot is around 4...and it isn't by any means low. It is louder at zero! I'm baffled. I have accessed the electronic boards, checked for obvious connection issues, broken wires, etc, and everything looks fine. I used contact cleaner on both output jack assemblies and it looks like the bypass circuit on the jack assemblies close as intended when the jack goes in. I burnished the contact zone for the bypass circuit connection just in case there was any gum interfering, etc. Totally stumped. I'm willing to entertain any/all theories.