Windows 10 Feature Update Fails with Error = 0x80240022. Commit Result = 0x00000001 (or 0x80070522: A required privilege is not held by the client)

Using Bryan Dam's excellent Software Update Installation Failures by Update report, I discovered almost a thousand systems failing to apply the 1709 Feature update that I'd deployed via ConfigMgr. 

The error was seemingly random since over 3000 systems had successfully updated. All were 1607 (though I think this symptom could apply to other versions).

The error was either:

0x80070522: A required privilege is not held by the client

or

0x80240022. Commit Result = 0x00000001

The feature update would not install. Moreover, it failed almost instantly in Software Center. UpdateDeployment.log and WUAHandler.log both reporting 0x80240022.

Cue lots of log-trawling and internet searching (and even an opened case with Microsoft) all without success - shame on you Microsoft! I then noticed that using 'Check online for updates from Microsoft Update' was also immediately failing; usually with error 0x80070006. This led me to this site: https://superuser.com/questions/1195688/windows-update-error-0x80070006

Comparing the sc query wuauserv results for broken and working systems showed a difference in the TYPE:

Broken

 Working

I set the process Type to be shared using: sc config wuauserv type= share

Then restart the computer (or you could use sc sidtype wuauserv none if you're doing all this via a remote command prompt using PSEXEC!)

The Feature update then installed successfully from Software Center with no errors.