Check the switch tabs? where the wires are soldered in.

When in switch test, if you bang on the playfield with your fist, does it show the switch closing?

So if you press the right flipper button on switch test, you don't get any indication that the switch is closing? If that's the case I would investigate there. Either the switch isn't gapped properly or it might already be stuck closed, both of which will not cause any reaction if you press the button. When in switch test, physically press the two switch blades together to see if you get something (if open) or inspect and separate them if it looks already closed.

If you've got Stern tech on the line, they will get you back up and running again. I have to look on my game but I would potentially check the connector of the flipper switch to whatever board it runs to. It sounds like its either a connector issue or a switch issue. I would personally focus on why the game isn't registering a switch when the contacts are touching, whether it's a physical obstruction or there is a connection issue.