Fast Startup is quite handy functionality in Windows 10 that reduces the boot time of a system. Unfortunately, the feature obstructs Windows update leading to fail installation and throw some error. Microsoft has decided to address the Fast Startup issue in context of Windows update in future version.

You might have noticed that Windows updates are not successfully installed subsequent to shutting down your system. The reason behind this resistant behavior is the enabled Fast Startup. The same doesn’t occur when you restart your computer.

Fast Startup bug Windows 10 bug will be fixed

The Fast Startup is a combination of hibernation and shut down that saves some of your system files. The files load as they were in the next startup and thus boot time is lessened. Clean install of Windows 10 turns the “Fast Startup” on as a default configuration in Power options Settings resulting in Windows update failure.

After a shutdown when you turn on your system, commonly, a patch requires dealing with the pending operations for a successful installation. The operation couldn’t be dealt with without a complete shutdown. Consequently the installation of Windows update fails only because of the enabled fast startup.

Therefore, if you want to install the patch you must have to effectuate a full shutdown of your computer.
Either you can restart the system to complete the operation pending.

The same is also affected when Microsoft Endpoint Manager Configuration Manager aka MEMCM is used. So Microsoft has planned to address this issue in a future Windows version.

Source – Microsoft help.