Everything works on Shore Power, Nothing on Generator

If you have an energy management system, it MAY be preventing your generator power from reaching the coach if it is too low. It can be too low(zero) if the generator circuit breakers have tripped or if the generator is out of adjustment for the proper voltage and frequency.
Your transfer switch is working otherwise you would not have any power to the coach from shore power. ALL input power goes through the transfer switch, whether it is on generator or shore power.