Are you running a Third Party Anit-virus? i.e. anything apart from Windows Defender then chances are that because of the recent Meltdown and Spectre Security issues, it has some compatibility issue which will restrict your Windows 10 PC to get the patches to fix that issue.
While Microsoft has already rolled out patches for the major architecture flaw through a cumulative update and is available for Windows Insiders, it seems even companies behind the Anti-virus software need to update their software. As per Microsoft, that anti-virus software makes unsupported calls to Windows Kernel Memory. It can also lead to unbootable devices if forced.
Microsoft Support page has a good explanation of this issue that Anti-Virus Software need to update following their support page.
The compatibility issue arises when antivirus applications make unsupported calls into Windows kernel memory. These calls may cause stop errors (also known as blue screen errors) that make the device unable to boot. To help prevent stop errors that are caused by incompatible antivirus applications, Microsoft is only offering the Windows security updates that were released on January 3, 2018, to devices that are running antivirus software that is from partners who have confirmed that their software is compatible with the January 2018 Windows operating system security update.
If you have not been offered the security update, you may be running incompatible antivirus software, and you should consult the software vendor.
According to the support page, this is registry key the Anti-Virus software need to update:
Key=”HKEY_LOCAL_MACHINE” Subkey=”SOFTWARE\Microsoft\Windows\CurrentVersion\QualityCompat” Value=”cadca5fe-87d3-4b96-b7fb-a231484277cc”
While you can add those keys manually, but we strongly recommend not to do so and ask your Anti-Virus company to update their software. Microsoft is working closely with antivirus software partners to ensure that all customers receive the January Windows security updates as soon as possible.