Windows 10 crashed after update and is now unbootable

dalchina said:

I first booted up from cold early this morning.
I did a restart at lunchtime- pending update.

The task seems to have run on the 2nd event

Yes, that's what I see too on my test machine. A cold start did not run the task no matter how long I left it running after that. Then I did a Restart today and it ran shortly after that. In my case it didn't change any files in Regback though.

Normally mine updates the files on the first boot.

Question seems to be, what's different between 1803 and 1709? Or is has this backup been rendered fundamentally unreliable?

If attempting to back up the registry at startup was the problem, then you might think running it manually would succeed- I've seen that succeed once, when there hadn't been a backup that day.

MS could have changed the action, or if it's simply a feature that has become unreliable because of other OS changes, it's now effectively been made obsolete, ineffective. Deliberate or incidental? Is there any way to find out?

It's curious that System Restore is quite frequently not enabled on PCs, so if this isn't available either as a sort of 2nd rate last ditch option, repair options become more restricted.