One possibility is there’s a Scotchlok splice somewhere in the circuit causing the problem. The possibility that it’s in an area that you can even see to know that it’s there are slim. They are often hidden behind the wall and ceiling panels of RV’s during manufacture.
Here’s a link to a topic of mine where I was lucky enough to be able to find one a few inches away from a light fixture that had been giving me problems. I still had to cut a hole in the ceiling to fix it though.
Truck Camper Scotchlok Fix