A Windows 11 cumulative update (24H2 or 25H2) downloads normally and asks for a restart. During the reboot phase the installation stalls at around 35–36%, displays the “Undoing changes” message, rolls back, and Windows Update history reports:
0x800f0922The update is offered again on the next check and fails in exactly the same way. Disk Cleanup, sfc /scannow and the Windows Update Troubleshooter change nothing, because the partition causing the failure is not the one they clean.
Supporting symptoms that confirm the pattern:
- the failure happens only during the reboot phase, never during download;
- free space on
C:is plentiful (tens or hundreds of GB); - the same update installed without issues on other machines from the same batch.
When this article applies. Error 0x800f0922 has several distinct causes, covered separately on this site: system repair commands (DISM/SFC), Registry settings, firewall rules, Windows Features (.NET 3.5) and UEFI Secure Boot. This article covers the remaining cause, and the most common one in 2026: insufficient free space in the EFI System Partition. If you have already worked through the articles above without success, and the failure occurs consistently at around 35% during reboot, this is the right place.