If it was my game I would replace the switch. I'm assuming you don't have replacements but order them now from pinballlife. They come with a diode attached for about $3.50 I believe. You are going to need them in this hobby.

In the meantime I would look at each switch on the areas I highlighted. Check the wires and the diodes to make sure none are broken off. These switches are daisy chained to one another. A broken wire at another switch could affect others down the row or column....like christmas lights. If everything physically appears fine test each one of those switches in "Switch Edges" in the test menu. You should hear each switch register with a beep and see it on the dot matrix display when activated. If one doesn't work it could be a bad diode at that switch impacting others (Switch 57) down the line.

Buy switch here.
https://www.pinballlife.com/microswitch-with-diode.html

If those options don't work it could be a switch matrix issue on the board. There are ways to test that also but you will need a diode and with a piece of wire soldered to the end. You can pull the switch matrix connectors (one for columns, one for rows) and touch the wire end to one and diode to the other and you should see the switches register in Switch Edge Tests. I don't think this will be a problem as it sounds like only one switch is out.
Wh20 Switch (resized).JPG