The issue affects Windows 10 v1809 and Windows Server 2019 systems with UEFI Secure Boot. The issue has been root caused to a problem with catalog file validation and whether it shows up is highly dependent on set and order of signed components in the boot path so it is not predictable when or whether a system will hit this issue. Only users of the Windows 10 Education and Windows 10 Enterprise will be affected by this software bug. Microsoft is currently working on a fix which will be released through Windows Update.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-system-guard-launch-causing-blank-boot-screens-in-uefi-pcs/