Switches can be "normally open" or "normally closed". Most are normally open, and close when the ball is over the switch arm or sensor. I like to roll the ball over the switch trigger to see, as compared to just lifting the play field and manually triggering the switch (a switch can be good but needs to be adjusted to actually work). So having the balls removed does not make it more accurate, testing the switches by using a ball to activate them is. If the balls are in, you should see the trough switches closed. Take a ball out and roll it around it test mode. The switch will be named as it is activated on the screen. If doesn't activate, check to see if works manually. If it does, adjust the switch. If it doesn't, buy a new switch.
I had a problem with VUK because the switch needed to be adjusted underneath. My guess is the switch where the ball drops into scoop after launching is not registering the ball was there. It just sees it in the slot scoop and fires it out. Hope that helps.