My Onan 10K sporadically does the same thing on my coach. I have found that if I wait a few minutes and try again, the gen cranks and starts as normal. Also, I find sometimes that if I fully extend the gen slide and use the direct start switch on the gen, it will usually crank. I have thought perhaps I am losing pressure in the fuel line? Not sure and it’s hard to diagnose as it doesn’t seem to do it all the time.