If it’s in a slide, there should be a chase in the basement where the wires connect, I’d look there.
The lights are usually run in a daisy chain. If the first in the parallel is not connected, none will work. We had that problem in our previous Phaeton, bathroom lights would only work once in awhile. Finally one day out of frustration I banged on the ceiling near a light and they all came on, pulled out that light and found the wires were not securely fastened.
2018 Allegro Bus 37AP
2014 Phaeton 40 QBH (sold)
2018 Jeep Recon