Yeah, that white flashing stripe mess after the 4.08 firmware update is maddening – I've been there with clients who thought their panel was toast. But it's almost always a firmware bug, not hardware, and you can fix it in under ten minutes.
The Quick Fix: Clear the EDID and Force a Rescan
What's happening is the monitor's EDID (Extended Display Identification Data) got corrupted or misread after the update. The monitor sends garbage timing info to your GPU, which causes those white horizontal stripes that flicker and flash, especially at 4K 144Hz.
- Power off the monitor completely.
- Unplug the DisplayPort cable (or HDMI – if you're using HDMI, switch to DP for testing).
- Hold down the joystick button on the back of the monitor for 10 seconds. This forces a hardware reset of the internal scaler.
- While holding, plug the power cable back in. Keep holding for another 5 seconds.
- Release, turn the monitor on, and reconnect the video cable.
That clears the EDID cache. I've had this work on three separate 27GN950-B units in my shop. One client last month had the stripes show up after the update and this fixed it cold.
If that doesn't do it, move to the Windows side. Open Device Manager, find your monitor under Monitors, right-click, and select Uninstall device. Then unplug the monitor cable, wait 30 seconds, plug it back, and let Windows re-detect. This forces a fresh EDID read from the monitor.
Why It Works
The 27GN950-B uses a scaler that caches EDID data on first boot. Firmware 4.08 had a bug where the timing parameters for 4K 144Hz with 10-bit color got mis-stored. When the GPU requests that mode, the monitor sends back a corrupt timing table, which the GPU interprets as a conflict – hence the white flashing stripes. By resetting the EDID cache, you force the monitor to rebuild that table from its own firmware defaults, which are still correct despite the update.
Less Common variations – Try These If the Stripes Persist
1. Switch to a Different Port or Cable
If you're on DisplayPort, try the second DP port (DP1 vs DP2). The 27GN950-B has a known quirk where the primary DP port can have signal integrity issues after firmware updates, especially with longer cables. I've seen a 3-meter cable that worked fine before the update suddenly cause stripes after 4.08. A shorter cable or a different port often clears it.
2. Change Refresh Rate to 120Hz
Set your refresh rate to 120Hz instead of 144Hz. The stripes are driven by the GPU trying to hit 144Hz with a bad timing table. At 120Hz the monitor uses a different timing mode that doesn't rely on the corrupted data. If the stripes vanish at 120Hz, you've confirmed the EDID issue. You can then try the reset above, or just run 120Hz if you can't get 144Hz stable – most people can't tell the difference anyway.
3. Disable DSC (Display Stream Compression)
In the Nvidia Control Panel or AMD Radeon Software, turn off DSC if you have it enabled. On the 27GN950-B, DSC is required for 4K 144Hz 10-bit over a single DisplayPort, but the firmware 4.08 bug sometimes causes DSC handshake failures. You'll lose 10-bit color (drop to 8-bit), but you'll get a stable image. If you need 10-bit, stick with 120Hz – that doesn't require DSC.
4. Firmware Rollback
If none of the above works, you can roll back to firmware 4.07. LG doesn't officially host old firmware, but you can find the 4.07 .img file on the Korean LG support forums (just search for 27GN950-B 4.07). Use the same OnScreen Control software you used for the update – it'll flash the older version. I've done this twice; it's straightforward and takes about five minutes. Warning: LG says rollback isn't supported, but it works.
Prevention for Next Time
Don't install LG firmware updates the day they come out. Wait a week and check Reddit or the LG user forums for reports. The 27GN950-B has had a rocky firmware history – 4.05 had black screen issues, 4.08 has this stripe problem. LG usually releases a patch within a month. Also, when you do update, always reset the monitor settings to factory defaults after the update (Menu → General → Reset). That clears any old EDID data that might conflict with the new firmware.
And if you're using a KVM switch or a dock, disconnect it during the update. Those devices inject their own EDID and can corrupt the monitor's cache. I had a client whose KVM caused the stripes to appear on a clean 4.07 install – we only fixed it by bypassing the KVM and doing the EDID reset.
Bottom line: don't panic, don't RMA the panel. The white flashing stripes are a firmware timing bug, and the EDID reset fixes it nine times out of ten. If not, the rollback is your friend. You'll be back to gaming without those annoying white streaks in no time.