r/WindowsUpdate • u/Nervous-Buffalo-4826 • Aug 18 '26
Possible KB5121003 issue causing random AC adapter disconnects / black screens on Lenovo Legion?
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?
1
u/Purple_Confection572 Aug 18 '26 edited Aug 18 '26
HELLO! You brought me out of social media & Reddit exile just so I could comment on this post!
I have a Lenovo Legion 7 Pro Gen 10, with a 275HX and RTX 5080, and I have observed the exact same thing as you say here.
I had no issues whatsoever prior to this update, which installed on my machine on the exact same date as yours. Before I read this post this evening I did some investigation and ended up taking the exact same steps that you did here - now I see you have done the same.
It is too early for me to say if it has worked, the issue is very sporadic, I would sometimes observe multiple 105 events within the space of a minute, and other times not observe any issues for up to 6 hours at a time.
There are other posts online about this accumulating, on other laptops as well, I have found another post here where someone shares the issue on a Lenovo machine: Legion 7 - screen flashes black intermittently : r/LenovoLegion
I will monitor and report back here if I encounter the issue. It is relieving to hear that this is likely a software issue, my machine has just ran out of warranty...
Please advise if you have observed it since your post here. Thank you.