I can achieve normal operation of both slides by moving the touchpad connection for the full wall slide's touchpad from controller to controller. (This used to be the touchpad connected to the living room slide, so I know both touchpads are good.)
So there appears to be a special power disconnect inserted into the circuit for the living room touchpad itself. All other functions of the living room slide controller are normal.
Our ex sofa is still the suspect. There's a big wad of wires with multiple connectors that ran to the sofa that, you would think, would only have needed 12v power to drive the motors that reclined it.
Wish I hadn't thrown away the couch, but we hated it and it was clutter in the garage.