LG Ultrafine 5K M1 Mac spurious vertical shift in a 2 inch band on screen

I recently got a M1 Mac Mini, and have been using it with my 2019 LG Ultrafine 5K display (made in ¡Mexico!). Previously I used it with my Intel-based MacBook Pro with no problem at all, though there is one problem that I keep on hitting with my new M1 Mac. At times during boot somehow it creates a permanent vertical band in which every pixel is shifted from its position by a few points in Y-direction. It happens randomly, and unless I reboot my computer the effect doesn't go away. The vertical band appears around center of screen. Interestingly, if I take screenshot or record a QuickTime video when the problem appears, it does not seem to appear after reboot. So the problem is not recordable using built in screen recording applications. I will take a picture from my phone camera next time around for the Apple team, I wonder if anyone else in the community has had similar problem? I have done my part by filing the bug to Apple, but have received no response.

Mac mini, macOS 11.1

Posted on Dec 26, 2020 10:19 PM

Top-ranking reply

dre1138

Level 1

4 points

Posted on Jan 23, 2021 11:24 AM

Hi Ross,

I can confirm that using the USB-C cable seems to avoid the problem.

I have an M1 Mac mini and a LG UltraFine 5K monitor that was purchased in November (so presumably it's the latest incarnation). It came with two cables:

Thunderbolt 3 (USB-C) with white lightning bolt symbols at each end
USB-C cable

I've also tried a USB-C cable purchased at a local store. Here's what I've found:

The LG provided Thunderbolt 3 cable sometimes shows the vertical band of shifted pixels. The problem can be induced or fixed by sleeping the monitor via a hot corner, though it might take a few tries.
The LG provided USB-C cable does not show the problem. I slept the monitor and canceled logins to get a black screen a couple of dozen times and could not reproduce it.
The "store bought" USB-C cable does not work at all. It does not drive the monitor - the monitor stays black. That avoids the problem but it's a poor solution. ;-)

As you've pointed out, the sacrifice with the LG provided USB-C cable is that one maxes out at 4K (3840 x 2160).

I'm going to call Apple again to see where they're at with this.

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LG Ultrafine 5K M1 Mac spurious vertical shift in a 2 inch band on screen

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