From what you describe it sounds like a problem with the park's supply of power. The low voltage could be due to a variety of factors but that really isn't important. It sounds like your rig did exactly what it was supposed to do. And so did you :)
The 50A service is 2 - 120V "pipes" of power and it sounds like 1 of them had a problem. The 30A service is 1 - 120V "pipe" and it was clean in your situation. Keep an eye on things your next time plugged in to 50A service to be sure there isn't something wrong with your equipment. From what you describe a problem with the park power is by far the most likely.