Windows 11 update install failures are reportedly happening again – and it’s breaking the built-in antivirus

Windows 11 has reportedly run into problems with its latest cumulative update, with the upgrade failing to install for some folks, and breaking Microsoft Defender in other cases.

Windows Latest has rounded up the latest batch of complaints regarding a cumulative update for Windows 11, in this case KB5029263, which is the mandatory upgrade for August.

As mentioned, some users are reporting installation failures with KB5029263, and the other annoyance here is that the failed update keeps offering itself over and over, constantly lurking as a red dot (update pending warning) on the taskbar (system tray).

Readers of Windows Latest have complained directly to the tech site about this, and there are affected Windows 11 users venting on Microsoft’s Feedback Hub.

On the Feedback Hub there are also scattered complaints of some more serious gremlins in the works with this August update. That includes the update getting stuck before it completes (and getting stuck again on subsequent installation attempts), and also File Explorer failing to work (meaning you can’t explore folders on the desktop).

KB5029263 is apparently also messing with Microsoft Defender, Windows 11’s built-in security app – which now ranks pretty highly among the best free antivirus – in some cases. Some users are seeing the following error when opening the app: ‘Unable to log into Microsoft Defender.’

Analysis: Defender fix is inbound, apparently

On the last point, Windows Latest reckons that this error could be the result of a clash between the security fixes in the August update, and a separate new update for Microsoft Defender.

While Microsoft hasn’t officially acknowledged any of the above problems, including the apparent cases of Defender coming off the rails, Windows Latest claims it talked to a support engineer at the company. That Microsoft employee confirmed the issue and said it will be fixed by an update soon. (An update to either Defender, or one applied to the OS via Windows Update, but one way or another, a cure is seemingly in the pipeline).

The mentioned installation failures are nothing new, and it seems to be depressingly commonplace these days that some Windows 11 PCs will fail to successfully run the update process. This may be a small minority affected, but it’s a frustrating situation to be caught in – as you are, of course, left without all the latest security fixes. Those are important to say the least.

The other vital element provided by KB5029263, at least for those who have been affected by the issue, is the fix for a bug causing huge slowdowns with some SSDs (or at least this cures the majority of cases, it seems). You might own one of the fastest, best SSDs out there, but with its performance levels cut in half (potentially), it won’t look so clever. And if you can’t install the August patch to (hopefully) smooth over the issue, that’s going to be pretty irritating.

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