Which game is this?

Thanks for posting the diagram. Notice the wire colors are labeled for each vertical column and horizontal row. You'll see the problem switch will have at least 1 green/yellow wire and at least 1 white/red wire. As gutz said, each of those wires will also daisy-chain to to other switches in the same row (the outhole switch, left return lane switch, mcfly switch, and M drop target switch will all have at least 1 white/red wire) or the same column (both other doc targets, spinner, lock vuk, left ramp, right ramp will have at least one green/yellow wire).

You want to check all those other switches that share the same column or row as the problem switch, and make sure the wires and diodes are firmly attached on all of them.

Be sure to check that the diode is firmly connected on each switch too. I usually give each wire and diode a gentle tug to make sure they're firmly connected to the solder lugs on each switch.

Filing/sanding isn't recommended because it can damage the gold plating on the switch contacts. You can safely clean the contacts with isopropyl alcohol and a q-tip and/or wet a business card with iso alcohol and pull it between the contacts to clean them.

Could just be a bad switch. You can test the switch for continuity with your meter. You'll need to push the switch contacts together with your meter leads hooked up to it, so it may be a little tricky.

Maybe one of the solder lugs from the switch was touching something it shouldn't have been and removing and reinstalling may have alleviated the issue? I think the lamp being out was probably just coincidence. As long as it works!

Glad you got it sorted out! Enjoy!