The fact the you filed your switch may be the issue, you shouldn't file SS switches, use an eraser to clean them, only EM should ever be filed and even then gently. But I know the cabinet switches can get pitted really bad. Since you'll be replacing the switch this will probably fix your issue. But I'd measure the resistance on that right flipper coil and check/replace the diode on the coil. You might want to check any other switches that you've filed.