Works for me!
This failing to finish the update problem surfaced last week among some of us Windows Insiders (testers) and we reported it to Microsoft using our direct link for feedback. We described what was happening and not happening. An update like that usually ends with a short process of "Working on updates....%%%" during which it goes from 0-30%, reboots, then completes the 30-100%. This one wouldn't go past 21% before rebooting. Then it repeated the same 0-21% after the reboot, then rebooted again, and announced "We couldn't complete the update. Restoring your previous...." - like I couldn't tell it had already failed.
After I tried 30 or more times over two days, while trying various attempted cures each time, and nothing succeeding, I gave up. I installed my former Windows 8.1 Pro instead, ending 1 year, 10 months, and 16 days of testing Windows 10. Overall, for me, it was more of an aggravation than a pleasure. It has features I didn't want, but couldn't remove without crippling the system. Windows 8.1 isn't as bad, and it will be supported for several years yet. Maybe by then, Microsoft will have the bugs out of Windows 10.
Some time ago, Satya Nadella, Microsoft's CEO, said he wants us to "love our Windows". I do. I just don't love the same version he does. Probably because I'm not being paid to love any. And possibly because I'd rather be using my Windows rather than trying to fix it. That's not my job!