The Fast Startup feature in Windows 10 is enabled by default if applicable. Fast Startup is designed to help your computer start up faster after you shut down your computer. When you shut down your computer, your computer actually enters a hibernation state instead of a full shutdown.
When comes to Windows updates, some patch installation could require pending operations being processed during the next Windows startup that follows a full shutdown. Without a full shutdown, those pending operations won’t be processed. As a result, these update installations will not complete. Full shutdown only occurs when you restart a computer or when other event causes the computer to process a full shutdown.
In order to make sure Windows updates that require pending operations being installed properly, you have to restart your computer to complete the installation.