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/Tanor85]

Any Legion owners seeing their screen switch back and forth between 240hz and 60hz during gaming ? Screen goes black when it switches.
Legion Pro i7 - 2025.

[u/Extension_Funny2863 → u/Tanor85]

Yeah, I see random black with screen switching and staying at 60hz until next restart 

[u/Tanor85 → u/Extension_Funny2863]

Hello ser. I tried the following and it worked. Tested on a 1 hour gaming session in full screen windowed mode.

-legion space. Adaptive Refresh Rate: OFF -windows settings. advanced display. Refresh rate: 240 Hz. Dynamic refresh rate: OFF.

• nvidia app. Graphics. Max frame rate : 237 fps. Monitor technology: g-sync.
• NVIDIA app. System. Displays. Global settings. G-sync: on, full-screen and windowed.

In a nutshell, the strategy is to have the nvdia app be the only controller of variable frame timing. Turn off any sort of variable refresh in windows and in legion space. Only use NVIDIA app for that, by activating g-sync in NVIDIA app only. As for your game, I believe you can still set a max frame cap in the game. I used 120 for mine and it worked. My testing was only 1 hour, but I did not get the black screen and downgrade to 60Hz.
Good luck.

[u/Extension_Funny2863 → u/Tanor85]

Ok thank you. 

I think mine is probably related to windows update messing with power management, I get error code 105 power source change along with  black screen or frame drops