I have a 2020 Reatta XL t39 - If all the fuses and switches are on, go to bay 3 on the passenger side (you will see the inverter switch - I am assuming its on) and pull off the carpeted cover, behind this is the G9 Panel with all your slide-out connections, and controllers. This also supplies 12VDC to the 1st bay on the drivers side for almost everything in the cab. There are breakers there which do not look like your typical breaker, check them. There will be heavy wires that get connected (this is where chassis batteries and house batteries get connected, and charged). If the breakers are good, check each connection (I had a few lose ones that caused all sorts of random problems). You can use you volt meter to check and see if shore power, generator or the motor's alternator are charging properly. Good luck and let us know what you find.
Randy, Linda & Lily (mini pin dog) Central FL
2020 Entegra Reatta XL, 2020 Chevy Spark Toad
2021 Entegra Anthem B, on order