SO it could be an issue with the TS (Transfer Switch) the TS will detect that incoming AC voltage and switch between shore and generator power, when they fail you will get no power on one source, it can happen on shore or generator power. You will need to find the TS and when the generator is running confirm you have AC power going into it AND AC power coming out of it, if you have AC power going in and nothing coming out it has failed and would need to be replaced, if you do NOT have voltage at the TS then it is an issue with the generator, check the breaker again turn it off and then back on.
Location of the TS will vary, sometimes it is outside in a box next to the shore cord, other times it can be inside the RV, in back of the breaker panel, under the bed, etc. Try and follow BOTH the shore cord and generator cord as they will lead right to the TS.....
Hope this makes sense, if you have more questions or concerns please feel free to contact me, IF you are satisfied with my efforts please feel free to select a rating at the top of the page, it is the only way I get credit for helping, you can still follow up if needed... Robert