Manufacturers make thousands of parts a year. All it takes is a little air bubble inside one piece of steel, which cannot reasonably be detected, and you can have a break. It happens from time to time, luckily, it isn't widespread.
2016 Jayco Eagle HT 29.5BHDS (ordered 12/30/15, delivered 3/8/16)
2015 F-350 crew cab, short bed, 6.7L PSD, Pullrite Superglide 3300 hitch