That is exactly what happened to mine a few weeks back. my right paddle stopped working intermittently then after a tug on the wire is stopped completely.
I took everything apart to gained access to both ends of the wire bundle that runs through the wheel, checked it for continuity. I found 2 broken wires right as they exit the back of the wheel hub where they angle off. After I pulled the harness out the back a bit (its captive with in the hub and can only be moved back and forth a bit) the problem/break was obvious.
Finding the issue was easy, but soldering in a patch was a bit finicky since the wire is so small and it needs to remain small (after being repaired) so it still fits in the center of the hub and allows it to spin freely.
If you tried jumping this connection and it did nothing I would test the other shifters button with the jumper in place, that way you can run the same wiring through both shifter buttons and narrow it down to wiring or the button.