It appears that there is a "Catch 22". KB4526447 requires a "Restart" and you know what that means, you need to use one of the shutdown workarounds, which I failed to do. Will try the Pc's "Reset" button and see what happens.
Worked on both my Home desktop and Pro laptop. Both needed a long press on the power button after Restart now but after Powering on again the update completed and further shutdown/restarts worked fine.