FRST Fix applied.
Update was installed successfully then.
Pending restart performed - however, it got stuck at the blue screen "Working on updates / 100 % complete / Don't turn off your computer" for almost an hour now.
The only remaining thing is to clean up everything we used.
Right-click on FRST64.exe and rename it to uninstall.exe. Launch it and it will delete itself.
As for preventing the issue, unfortunately, nobody knows what can and will happen in regards to Windows Update, so I am afraid that I cannot offer any particular advice except saying that I'll happily assist you again should it be necessary.