The Windows 10 KB4507453 Cumulative Update released by Microsoft on July 9 is reportedly causing a restart notification loop on some of the computers where it was installed. Windows users were told to reboot their devices again to finish installing the update even though it was already installed. Microsoft has not yet publicly confirmed the problem, but not all users of Windows 10 version 1903 who install this cumulative update will be affected. The update information doesn’t include any info on changes made to the Windows 10 notification system or the update installation procedure that could be behind this glitch.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-kb4507453-cumulative-update-causes-restart-alert-loop/