A little late to this party but since everything works with your genset, my guess is one of two issues, both have been mentioned.
1. Campground pedestal. Since you said you had this problem at a previous campground, unless it's a coincidence, the pedestal is not the problem. That said, I would start there as it's the easiest to check. IMHO, your toolbox should contain two items...a voltmeter/continuity tester, inexpensive but take the time to learn how to use it, and a pedestal tester. Here's the link to one I made using parts from Home Depot...about $60 bucks...
50 Amp Pedestal Tester. This will check voltage on each leg, whether the pedestal is wired correctly and check for an open neutral.
2. Your power cord. This would be my best suspect to your issue. The type you have will determine how you can test it. If you have the twistlok type, plug it in and test the other end with your voltmeter. If you have a fixed cord, you'll have to open the transfer switch to test it.
Both of these items are the easiest and simplest to check. If they check ok, then move into the heavy stuff. Do the simple stuff first..Dennis