Cumulative update KB5001330 fails to install

Johnny_KimYour answer pointed me in the right direction to fix the error by myself.

In my case, the KB5001330 was installing successfully, then the computer restarted, then at 96% the update failed and rolled itself back, and after another restart i went to Windows Update to see the error number 0x800f0922. In my case, the reason for the failure was that my EFI partition was missing some files.

So, TL;DR: I fixed the error by replacing the \EFI\Microsoft\Boot directory on the EFI partition with the contents of C:\Windows\Boot\EFI.

The long story:

DISCLAIMER: this is technical, I do not take any responsibility, etc.

The EFI partition should contains the following directories:

\EFI\Boot

\EFI\Microsoft\Boot

\EFI\Microsoft\Recovery

... and if you dual-boot it may contain other directories, but that's irrelevant.

In my case the problem was, my EFI partition has got corrupted a month ago, and Windows, in its attempt to fix it, has broken it even more, the result being:

- some files and directories in \EFI\Microsoft\Boot went missing,

- in the root directory of the partition, several hundred files with randomly-numbered names have appeared.

This was preventing the KB5001330 update from installing.

So, first I assigned the drive letter to the EFI partition - it is normaly not assigned. I opened the cmd shell in administrator mode and entered "mountvol p: /s" (see here for details). The EFI partition became visible as the P: drive.

Then I removed all the randomly-named files from the root directory of P:\

Then I removed all the contents of the P:\EFI\Microsoft\Boot directory. Some of the files there were protected from deletion (in particular,BCD and BCD.log), so I just left them intact.

Then I copied the contents of the C:\Windows\Boot\EFI directory to P:\EFI\Microsoft\Boot. This way I restored the correct contents of the EFI partition.

Then I rebooted, to verify that the system still runs properly. (By the way, you do not need to unassign that drive letter P: - it disappearsafter reboot.)

Then I went to Windows update and proceeded to install KB5001330 again. This time it went smooth.

Note that the size of my EFI partition is 100MB; the standard size as created when installing Windows 10 from scratch. The size was not an issue in my case - I have 73 MB free on the EFI partition and it was enough to install KB5001330.

To reach my success, I used some information about restoring the EFI partition from this article. In my case it was not necessary to restore the whole partition from scratch, but if my solution does not help some of you, you might want to do the full restoration as described in that article.