Do you have a clamp ammeter? If so place it over the Hot of the same leg of your 20 amp breaker to see if you are reaching 20 amps or more of current
draw. If the current draw never exceeds 20 amps and the breaker still pops then the breaker is faulty. If you do reach or exceed 20 amps and the breaker pops then it is doing its job correctly.
You really do need the clamp meter so you can get an independent verification of how much current is being drawn from your generator
. Those cheap
little AC current meters on boats can go bad giving you a false reading.
Hey, it's better to have a breaker that pops at too low of a current than to have one which melts wire insulation
or damages your generator.