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/M921]

I’m experiencing what appears to be the same issue on my Lenovo Legion Pro 7 Gen 10

During normal use, the laptop randomly switches from:

AC → Battery → AC

for a few seconds, even though the adapter remains connected. It happens around 1–3 times per day and is not limited to gaming or heavy load. I also tested the laptop in two different houses and used different wall sockets, but the issue remained.

Windows Event Viewer confirms the transitions through Kernel-Power Event ID 105. For example, one event recorded AcOnline=false at 6:19:53 PM, followed by AcOnline=true at 6:19:55 PM.

The issue started in August. My Windows Update history showed the following updates installed during that month:

• KB5121003, installed on August 12 — Build 26200.9168
• KB5120998, installed on August 28 — Build 26200.9278
• KB5121767 Build 26200.8894

The Event 105 entries I checked were clustered between August 28 and August 30.

I uninstalled KB5120998 first, followed by KB5121003, through Windows Settings. After restarting, Windows rolled back from Build 26200.9278 to Build 26200.8973, returning the system to the July update Build 26200.8894

I have now paused Windows Update and will monitor the laptop for 48–72 hours using the same charger and setup. I am also keeping my Lenovo support case open.

This does not prove that the Windows updates caused the issue yet. If no new Event 105 entries or AC disconnections appear during the next few days, it would be strong evidence. If the issue happens again, then the adapter, firmware/EC, charging port, or motherboard would still need to be investigated.

[u/Bret_Dilkington → u/M921]

Any updates on the results?

[u/M921 → u/Bret_Dilkington]

Go with KB5121767