Bug Report: Cumulative Update / Preview Update fails with Error 0x800f0991 on Windows 11 25H2 images

[emilwojcik93]

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Provide a clear and concise description of the issue.

Description

When creating a custom Windows 11 25H2 image using microwin injected with the latest official drivers, Windows Update fails to install the May 2026 Preview Update (KB5089573) and Cumulative Update (KB5089549).

The update process hangs for a long time before eventually failing with installation error code 0x800f0991. Standard Windows Update repair techniques (like SFC and DISM) fail to resolve the issue, suggesting that a component stripped or modified by microwin during image creation is breaking the servicing stack dependencies required for this update sequence.

Steps to reproduce the issue.

Steps to Reproduce

1. Generate a custom Windows 11 25H2 image using microwin.
2. Integrate the latest official hardware drivers into the image during the build process.
3. Install the resulting OS on a device or virtual machine.
4. Check for updates via Windows Update and attempt to install KB5089573 / KB5089549.

Paste the full error output (if available).

No response

Additional context.

No response

[giuliotoplad]

I think It could be helpful if you share the full Log of Windows Update and the CBS one.
If you can, go to PowerShell and type Get-WindowsUpdateLog, It should generate the full Log file on the Desktop if I remember correctly.
The CBS Log can be found at C:\Windows\Logs\CBS.
Usually those logs shows what cause those problems.

[OneNot]

Same behavior, different update and error code.
The update: 2026-08 Security Update (KB5121003) (26200.9168) fails on my install.
My install is from an official Win11 image modified by MicroWin. (older version of MicroWin, I can't remember how old / what version)
Install error - 0x80070306 from Windows Update.
Windows Update Standalone Installer also fails to install it.

DISM healthcheck fails.
sfc finds nothing wrong.
I left it alone for a few days, then at some point the update seemingly went through, but the Settings app was fully broken after that. It would crash when attempting to open.
In-place reinstall of windows from a MicroWin image made from latest official Windows11 image (keeping files and apps) fixed the settings app, but the update is still not going through.

WindowsUpdate.log and CBS.log attached. (Zipped because CBS.log is massive)
logs.zip

Windows isn't my main OS so a full disk wipe and clean re-install is okay. Will probably do that next week. Hopefully that at least fixes the issue. I will report back.

It's possible this is unrelated to MicroWin, but I can't think of anything else this could be. I haven't done much modification of my system beyond MicroWin and (mainly recommended) WinUtils options, as far as I remember.

[OneNot]

I did a clean install from the latest official image, modified with MicroWin 2.0. Initially updates went through just fine, even the previously problematic 2026-08 Security Update (I think? It might have come with the image, but I think I saw it getting installed with the initial set of updates after the clean install...), but now I'm once again unable to install latest security updates.
This time it's 2026-09 Security Update (KB5124008) (26200.9445) and error 0x80073712.

This time DISM /Online /Cleanup-Image /RestoreHealth and sfc /scannow went through and supposedly found and fixed issues, but after a reboot, the updates still fail.

I also decided to try and reset my Windows update settings from WinUtils (I had it on the Recommended preset from WinUtils) to see if other updates go through, and indeed, other smaller updates went through just fine, such as Security Intelligence Update for Microsoft Defender Antivirus - KB2267602 (Version 1.459.219.0) - Current Channel (Broad) (which I'm surprised the WinUtils Recommended settings apparently pushed back...)

logs.zip

I might do another clean install at some point in the near future without MicroWIn and will report back if the issue appears with an unmodified image (well, mostly unmodified, I will probably use Rufus to insert a local user account).