Lenovo computers running an older version of Windows 10 (1607) may not be able to boot, according to reports.
Microsoft has acknowledged this and updated its guidance and known issues for the update page.
After installing KB4467691, Windows may fail to startup on certain Lenovo laptops that have less than 8 GB of RAM.
Restart the affected machine using the Unified Extensible Firmware Interface (UEFI). Disable Secure Boot and then restart.
If BitLocker is enabled on your machine, you may have to go through BitLocker recovery after Secure Boot has been disabled.
Microsoft is working with Lenovo and will provide an update in an upcoming release.