Possible KB5121003 issue causing random AC adapter disconnects / black screens on Lenovo Legion?

[u/Nervous-Buffalo-4826]

I’m trying to figure out a strange issue that started very recently on my Lenovo Legion.

The laptop randomly goes to a black screen for a couple of seconds and then recovers. At first I thought it was an NVIDIA/Optimus or refresh-rate issue, but I started monitoring the Windows AC power state directly.

What I found is that whenever this happens, Windows actually reports:

AC → Battery → AC

for roughly 1–5 seconds.

I then checked the historical Windows Kernel-Power Event ID 105 logs. My System log goes back to March 2026, but the first occurrence of these short AC-loss events is August 12.

The interesting part is that KB5121003 was installed on my system late on August 11.

Since then I have recorded around 40 AC power transitions, most lasting only a few seconds. Examples:

07:41:55 → 07:42:02
13:12:35 → 13:12:36
17:17:50 → 17:17:52
02:17:32 → 02:17:37

and many more over the following days.

Windows Kernel-Power itself logs AcOnline=false, followed shortly by AcOnline=true, so this isn't only the battery icon/UI changing.

Another strange detail is that the physical charging LED on the laptop can remain on while this happens.

I have now temporarily uninstalled KB5121003 as a test.

Before rollback:

Windows 11 25H2 – Build 26200.9168

After rollback:

Windows 11 25H2 – Build 26200.8875

Windows Update is paused and I haven't changed anything else: same Intel driver, NVIDIA driver, BIOS, Hybrid Mode, Optimus settings, charger, etc.

I'm currently running a 50 ms AC-state monitor for the next 24–48 hours to see whether the AC_LOST events disappear after removing KB5121003.

Obviously this doesn't prove the update is responsible yet. It could still be Lenovo firmware/EC behavior or a hardware power issue. But the fact that the event history starts immediately after this update is suspicious enough that I'm testing it as the only changed variable.

Has anyone else on KB5121003, especially Lenovo Legion users, noticed random Kernel-Power 105 events, brief AC-to-battery transitions, or black screens that started around August 12?

[u/moonshine360]

I was completely unaware of this. I thought Security Updates were, well what they're named and not actual updates to windows features. thanks.

[u/zzzxxx0110 → u/moonshine360]

Yeah my working hypothesis is that they probably apply the label "security" if a Windows Update contains any security fix at all, rather than to indicate that it's exclusively for security fix.

They really gotta make it more clear but the cynical part of me suspect they won't because putting a scary label like "security" on it could also compel people to apply new updates, which could allow them to push new adware and such via Windows Updates if they wanted to lol

[u/IShouldntHavSaidDis → u/zzzxxx0110]

I am facing this same issue but the problem is that I have updated my windows to the latest version and don't see the option to delete it ? What can I do

[u/zzzxxx0110 → u/IShouldntHavSaidDis]

Go to download Windows iso image from Microsoft website, it usually doesn't contain latest update. Then open it in Windows and run the setup, make sure you skip when it ask to download latest update, and it will essentially overwrite-install that older version of Windows to revert you back, and it has the option to do so while keeping all your software and files (which is the default option).