I have never seen 120 volt lights factory installed in an RV, however after market anything is possible.
Can you give a list of what does, and does not, work
Also you said you measured 120V on the breakers,, With reference to what (White bus or bare/green bus)
Some things to look at
MIcrowave, Air Conditioners and TV's work But outlets do not (GFCI(s) tripped)
NOTE: MIcrowave migbht be on a GFCI as well
NOTHING AT ALL WORKS
While unpluged.. Take a screwdriver (may need a #2 Square bit) and check all the screws, I mean ALL the screws in the power distribution panel... Several of mine were loose.