Windows 11 KB5124008 Problems: What KB5129195 Fixes — and What It Doesn’t

COMPUTER & TECH SUPPORT

I spent a good chunk of last week on machines that had been perfectly happy the Monday before. Same culprit every time: the September Windows 11 update, KB5124008, which arrived on the 8th and took a few things down with it. On the 14th Microsoft pushed an emergency out-of-band fix, KB5129195, and that repairs some of the damage.

Some of it. Here’s the part almost nobody is writing about, and the reason I rewrote this post: the thing still broken after the emergency fix is File History — the backup built into Windows. It stops working without telling you. The switch still reads On. I would rather you spent five minutes on that today than read the rest of this page.

What broke, and what the emergency update actually fixed

These are separate bugs in unrelated parts of Windows, which is what you get from an update Microsoft itself described as changing an enormous number of files at once. Not all of them will touch you. Find your row.

The backup failure is the one nobody is covering

Here is what is actually happening, because the mechanism explains why it’s so easy to miss. File History has two parts: a service that copies your files, and an interface layer that talks to it. Since the September update, that interface layer crashes on a .NET error — in Windows error reports the failing component shows up as fhuxadapter.

What you see is File History telling you to “Reconnect your drive” for a drive that is plugged in, that you can open, and that you can copy files onto by hand without any trouble. The drive is fine. Windows has simply lost the ability to manage the backup.

The failure mode is the problem. The switch still reads On. Clicking Turn off sometimes does nothing at all. The backup folder structure still sits there on the drive, so at a glance it looks like a working backup — it has just stopped gaining new files. The person who notices is the person who goes looking three weeks later, in the week they actually need it, and finds their newest copy is dated September 7.

So go and look, right now. Open the external drive in File Explorer, find the FileHistory folder, and click down through it until you see folders with dates on them. If the newest date is on or before September 8, your backup stopped that day. Copy your Documents and Pictures folders onto the drive by hand in the meantime. If you’ve never been certain your backup was real, this is the week to sort it out properly — I went through the three approaches that actually work in my guide to backing up a computer.

Why a bad update sometimes fixes itself if you just restart

There’s a mechanism inside Windows most people have never heard of called Known Issue Rollback. When a non-security change in a cumulative update turns out to cause trouble, Microsoft doesn’t have to pull the whole update — it can push a small signal from the cloud that switches that one change back off. Your PC picks it up in the background and it takes effect after a restart, sometimes within hours, sometimes closer to a day.

That’s why “have you restarted it a couple of times since Tuesday?” is a real diagnostic question and not me brushing you off. A machine that was misbehaving on Wednesday can be fine on Friday with nobody having touched it. It’s also why two neighbours with identical laptops get different results on the same afternoon — these rollbacks reach devices in waves. What it can’t do is undo a security change or repair a graphics driver, which is why it hasn’t helped with the Radeon problem.

If you’re staring at a black screen

Black screen after signing in, nothing but a cursor: try Ctrl + Shift + Esc to bring up Task Manager, then Run new task, and type explorer.exe. That gets a lot of people their desktop back, which is enough to install the fix or remove the update.

If that doesn’t work you’re into Safe Mode, and that’s the point where I’d stop experimenting — particularly on a machine holding the only copy of something. One more thing worth knowing, because it catches people who reach for the command line: this update ships as a combined package containing both the cumulative update and a servicing stack update, and the servicing-stack half cannot be removed at all. That’s why the old wusa /uninstall command fails on modern Windows. If the Settings route refuses to remove it, that’s a sign to stop rather than to start pasting commands from a forum, and a good moment to get hands-on Windows help.

And then come the phone calls

Every widely reported Windows problem is followed within a week by a wave of calls and pop-ups offering to fix it, and I see that cycle up here reliably. It works because the caller sounds informed — they name the update, they describe the symptom you actually have, and they’re calling precisely because the news made that symptom likely. The ask is always the same: let them onto your screen.

Microsoft does not call you. Neither does Dell, nor HP, nor your bank’s “security department.” Nobody legitimate discovers your PC has a problem and phones you about it unprompted. If a pop-up gives you a number to call, it’s a scam, without exception — close the whole browser rather than the pop-up. The same tactics arrive by email, which I covered in how to spot a phishing email.

When it’s worth calling me

Most people reading this need to do exactly two things — install KB5129195, check the backup drive — and nothing else. Worth a call: a machine that won’t boot or shows a black screen you can’t get past; a small office where Remote Desktop or a shared application went down and several people are stuck; a backup you’ve just discovered wasn’t running on a machine you depend on. Those are quick to sort out and expensive to leave sitting.

Not worth paying anyone for: one feature being awkward for a week while a fix ships. And if this has you thinking about blocking Windows updates for good — don’t. The compromised machines I see are almost always the ones months behind, not the ones that caught a rough Tuesday. If you’re running several Windows machines in an office, the real answer is staged updating so one bad patch never takes out everybody at once, which is part of what small business IT support is for.

Who I am, briefly

I’m Guy. I’ve been doing tech support on the Upper West Side since 2010 — homes, home offices and small businesses. When you call, you get me, not a call centre and not a different subcontractor every visit. That continuity is most of the value: I already know how your network is wired and which machine holds the backup.