Windows October Patch Day Faces Issues with Hyper-V VMs

Problems with Hyper-V have emerged in connection with Windows security updates from October Patch Day. Users report that the update prevents virtual machines from starting. Microsoft has not yet commented on the problem.

Virtual machines are not starting up

Apparently, only users of Windows Server 2022 and Server 2019 and the recently released patch day update KB5031364 and KB5031361 from October 10th are affected.

The problem is always the same: After the update, users may experience problems with Hyper-V on Windows Server installations. Virtual machines can no longer be started; only a corresponding error message is displayed.

There is currently no entry in the Windows Release Health dashboard, but that should only be a matter of time. Those affected are currently discussing solutions to the update problems in the Microsoft Answers forum.

“It turns out that the additional files in the folder with the VHDX files (.CBD = Changed Block Tracking; mrt = Microsoft Resilence Tracking; crt = Resilient Change Tracking) are causing the problem,” writes Born, referring to the user reports. “Deleting these files (apart from the .vhdx files) should resolve the error (without renaming the VHDX files),” it continues.

Alternatively, uninstalling the last patch helps. This means that you are back to the status as before the incorrect update and can wait for an official solution from Microsoft without making any changes to the system yourself.