I had an intermittent issue like this on one side of my
American Changer some years back. It was the push-in connections on the
door board at the top left corner. (your middle photo)
Take a tiny jewelers screwdriver and work them out and back in until the insulation on the wire is not interfering with the connection.
I had just converted over to CC Talk which required replacing all the components and one side had this problem. When I figured it out, I re-worked the other side too.
No matter how you anchor that cable down, the connections still get "worked" somewhat when you open and close the
door, so the connection has to be pinched really good between the wire and clamp jaws.