From Thurrott:
Microsoft Fixes Borked Windows 10 Update
Microsoft has issued a script that fixes a borked cumulative update for Windows 10 that gets stuck in endless loop of failed installed attempts. We also have some clarity, finally, on which users are impacted by this bug.
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“The update, when it does fail, is causing some machines to restart, often multiple times, as Windows 10 attempts to remove the failed update,” he explained. “Worse, after a restart, the file will attempt to install again resulting in the loop of failed install, reboot, re-install and failure again.”
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According to Microsoft, an issue KB3194496 only impacted “a small number of customers in the Windows Insider Program that were running a previous build of the OS.” In other words, this bug impacted people who had previously installed a Windows 10 Insider Preview build but then later reverted to the shipping version of Windows 10 version 1607 on that PC.
If you are still having this problem please check the article linked to for essential details.
If you have updated successfully to Windows 10 from an earlier version then does not apply.