After updating to Build 18912 on a 3rd computer with Windows 10 Pro (which initially appeared to be a successful installation) things have gone disastrously wrong.
An Embroidery software program that is use regularly did not work, (worked on Build 18898) so attempted to Go back to the Previous build 18898.
Go back to the Previous build was not successful.
Restarting opened the Advanced Startup Menu.
Trying these options one at a time, and finally a clean install, resulted in a complete mess.
On reboot, getting things ready, kept getting error message "computer restarted unexpectedly.... Windows installation cannot proceed, click OK to Restart". But by doing so I am now in a continuous loop of restarting. Restarting takes me straight back to the same problem.
Cannot start in Safe mode.
It appears that I need an installation disc to reinstall Windows 10.
This computer installed Build 18912 without any problems