"Virgin Galactic has remained tight-lipped over what happened"
Not so. They publicly explained that a slightly prolonged spell at an altitude with higher-than-forecast winds blew them a little off course. They also noted that such events are common enough in regular commercial aviation.
The FAA's concern has always been that they flew outside the tickbox. Solution: make the spaceplane tickbox bigger, and add edge detection to the procedures. But that needed a little time to confirm.