If the rumor about the train not making it around the tracks the first time empty is true, this will certainly not be the first time this has happened on a major coaster. Plenty of rides have these kinds of issues because of the way they are engineered. I wouldn't worry about it happening during operations though because they'll probably have made adjustments to ensure it doesn't valley under most conditions.
By the way, we are only hearing bits and pieces about the testing process, mostly from third or fourth party sources. Don't assume that what you read on here represents the actual testing that's going on. I'm sure there's been a lot more going on than we know.