This kind of problem is really difficult to diagnose remotely; I can think of dozens of things that might cause this. Make and model on the chargers might help.
Your generator's frequency is probably not the problem, as very few plain chargers are sensitive to this. I would, though, check the voltage with a good meter under normal operating conditions and make sure it is in the range 110-125 volts.
That said, my best guess is a combination of two factors: Chargers that don't like their outputs wired to their inputs (this type of charger really can't be used on a conversion) along with a ground and/or neutral wiring error that masks this behavior on shore power but not on the generator. This theory is easy to test if the charger can easily be removed from the coach.
Double-check that your shore ground is properly connected and that your neutral bus is properly isolated on shore service, and fully bonded at the generator. Also that whatever mechanism you are using to switch between shore and generator switches the neutral along with the hot(s).