Just Had Fun With This
A machine with a NVMe would download the Fall Creators Update, display the message "updating, do not turn off or reboot..." for half an hour and reboot. If the user stared at the screen at boot the error message "Something went wrong, but we won't tell you what" popped up for a split second before an odd, graphical pre-boot menu gave the option to boot normally. The process would then restart.
It turned out that there's a problem which causes the BIOS SMART test to fail, even though the drive works fine. This is reported to the operating system which fails without saying what is going on.
The problem can be "fixed" by disabling SMART in the BIOS. It sure would have been nice if the OS or BIOS had bothered to tell me what was wrong rather than having me aimlessly wondering the internet for hours and hours...