The mirror on my XF malfunctioned the 2nd day out of the box. My dealer told me it was most likely a shorted circuit on the board, a fluke, but, in any event, unacceptable. Within two days, I had a new XF body in my hands shipped from Copenhagen.
Never had an issue since and I have put about 10K shots on the camera so far.
Bathtub Curve Failures are terrible for everyone (client, dealer, manufacturer). However, across all mechanical equipment it is a reality. You're much more likely to have an issue in the first few days in than the same period of time a year later. It's things like solder jobs that visually look solid but which have some imperfection that causes an issue only a few days in; if the solder is done perfectly it will last essentially indefinitely, but if it's not perfect that won't necessarily show in the pre-shipping tests. Such problems are the arch enemy of QC folks, and I think Phase One has done a great job reducing them to a minimum, but you can never get to zero.
Phase One, of course, tests gear before it ships. But as a dealer we
retest it before shipping to the client, in order to avoid any "it didn't work when I received it" client deliveries (as well as make sure that the firmware is up to date and the individual components purchased all are working correctly together).
I always tell our clients that I can't promise they won't have problems.
Some percentage will, no matter the price point, the QC done, or the quality of the product. I can only promise we'll respond quickly and well if they do.