Hi Jadon! I checked my 12 volt breakers and the under cabinet lights are on the same breaker as the bathroom lights. I thought they were on the LR lights breaker. I don't know the setup for yours but my breaker panel is in the bedroom on the driver side. I have a switch panel on the front of the bathroom vanity that has 3 switches on it: vanity lights, fan and waterpump. If I had that problem with mine I would pull out that switch panel and look there. My thinking is that the power, comes from breaker 2, goes to the switch panel on the vanity, then a wire runs off that panel to the cabinet lights.
When you check for power with your volt meter, what are you grounding it to?