Microsoft has confirmed a Windows 11 update problem that can leave some users facing a black screen after signing in, with the desktop failing to load automatically, particularly on virtual desktop systems using FSLogix profile containers.The company added the fault to its Windows release-health documentation on September 24, saying it originated with the August 27 non-security preview update, KB5120998, and can persist on systems that installed subsequent cumulative updates. Microsoft has classified the problem as mitigated while it works on a permanent resolution.
Azure Virtual Desktop hosts using FSLogix have been the main environment in which the problem has been observed, Microsoft said. The failure appears more frequently with certain existing user profiles, an important distinction for organisations operating pooled or non-persistent virtual desktop deployments where profiles are stored separately and reattached when users sign in.
Affected sessions can display a black screen immediately after authentication because the Windows desktop shell does not start as expected. Users may remain unable to reach the desktop until the session is started manually. Application event logs can also record crashes involving Windows Explorer, or explorer. exe, the process responsible for much of the Windows graphical shell.
The problem affects Windows 11 versions 24H2 and 25H2 through KB5120998, whose corresponding operating-system builds are 26100.9278 and 26200.9278. Reports also cover systems that installed the September 8 security cumulative update, KB5124008, indicating that the later servicing package did not eliminate this particular sign-in failure.
Microsoft has provided a Known Issue Rollback, or KIR, to help managed environments restore the Windows behaviour changed by the problematic update. KIR is a servicing mechanism that can reverse a specific non-security change without requiring administrators to remove the entire cumulative update, allowing security fixes in the package to remain installed.
For enterprise-managed devices, administrators can deploy the rollback through a special Group Policy available from Microsoft. The company says organisations using affected Windows versions should install and configure the policy for their environment and restart devices as required for the mitigation to take effect. A permanent correction is planned for a future Windows update.
For individual sessions already stuck at a black screen, Microsoft says users can manually launch Windows Explorer. Task Manager can be opened with Ctrl+Shift+Esc, after which the user can select the option to run a new task, enter explorer. exe and start the process. This can restore access to the desktop but is a workaround rather than a permanent repair.
Citrix has separately acknowledged black-screen failures on desktop operating-system Virtual Delivery Agents after installation of KB5124008 or KB5120998. It said environments combining Citrix Virtual Apps and Desktops with profile-management technologies including Citrix User Profile Management or FSLogix could continue to encounter the symptom even after applying out-of-band Windows updates issued for a separate Remote Desktop Services problem.
That distinction matters because Microsoft has dealt with several Windows issues during the September update cycle. An out-of-band update addressed instability in Remote Desktop Services, but Microsoft’s release-health documentation states that the black-screen and desktop-loading fault associated with KB5120998 remains a separate known issue.
The newly acknowledged fault is also distinct from another KB5120998 problem that caused some Windows desktop backgrounds to appear as a solid black colour. That earlier personalisation issue affected Windows 11 versions 24H2 and 25H2 because desktop settings failed to load correctly. Microsoft resolved it with the September 8 security update, KB5124008, and later releases.
FSLogix is widely used in virtual desktop deployments to place user profiles in virtual hard-disk containers that can follow users between session hosts. Microsoft released FSLogix 26.08, version 3.26.826.17182, on August 31 with security, stability and data-protection fixes, but its documentation separately lists the September black-screen-at-sign-in problem as an issue still being addressed.
Topics
Technology