I've learned the hard way to always clean the coating off of all new switch contacts (EOS, flipper buttons, pop bumpers etc). I use a 3/4" wide x 4" long strip of 600 grit sandpaper folded in half (so there's sandpaper on both sides). Hold the switch contacts closed with the sandpaper between them and drag the sandpaper strip a few inches. Do this once or twice and it should be good. Check for continuity with the mulitmeter afterwards to confirm good contact.