I haev this problem! For me it's a strip about 2 inches wide, down the middle, one pixel higher than the rest of the image. I am using an LG 5k monitor, and I have been unsure if it's a problem with the monitor or the machine. I'd love to know what kind of monitor you are using; this gives me hope that it might be an apple bug that will get fixed eventually.

I also have this problem--also an LG 5K. Disconnecting and reconnecting seems to fix it for now.

No idea if it's the monitor of the laptop, but it's the exact same problem and hopefully hardware doesn't glitch in such a consistent way and it can be fixed in software.

I have an LG 5k, too! And it only happens on that monitor - my LG 4k over HDMI is fine.

It's because the 5K monitor is actually two monitors taped together ("multi-stream transport").

It is two streams but it actually isn’t MST. It’s two independent HBR2 links; MST would have been two streams over one HBR2 link, which doesn’t have the bandwidth for 5k.

YES -- it's not just me! At first I thought my monitors were somehow broken (which is unfortunate as I paid a bit extra for name brand LG). I suspected something, as each monitor is plugged into an M1 computer (one's a Mac mini M1 and the other a MacBook Air m1). Both exhibit the visual problem you describe on a random basis.

pairing this with another comment by myself (about multi-monitor support beyond only one external monitor). I wonder if this is the main reason that Apple didn't support more than one external. Does the issue exhibit itself even more when additional monitors are connected? To be clear it never occurs with my main MacBook Air screen (only the external).

Just as a data point, I have an MBP M1 and an LG external monitor and this has never happened to me in almost 6 months usage.

I didn't mention this but it didn't happen initially, only after a couple months did the random screen errors happen. And power cycling, disconnecting/reconnecting/changing cables, etc to the monitor changes nothing.

I have an Acer Predator that has this issue (Whether using my Mac or PC attached.) Power cycling the monitor makes it go away. Basically the left side of the screen is shifted one pixel higher than the right side of the screen, making a vertical line down the middle where the shift changes.

in my case power cycling does not change anything, could be a separate issue for you. In my case it is also retaining a "ghost" of previous pages I've had open. It does eventually go away (and most of the time is not there).

I have zero weirdness at all. It just works perfectly all the time.

Neither monitor supports Thunderbolt. But I run off of a USB-C to Display Port cable and one is using the HDMI port. Both run at 60Hz as it is HDMI 2.

I run from display port to usb-c adapter -- I wonder if it is my adapter which is a simple Cable Matters adapter (which gets somewhat warm). Be nice if you shared what adapter you're using for comparison.

I don't have an M1 machine, but I have had periodic weirdness on external monitors (of every flavor) when waking from sleep on all the Mac laptops I've owned over the last 10 years.

that is ... bad luck. Or I have really good luck (having used mac's for over 20 years). This situation is a first for me (and in my case happens during normal usage, ie not upon waking) - though given Apple's recent track record screams buggy software

I have this happen on my Windows PC every now and again. It’s on the monitor that’s hooked up via DisplayPort.

I have run into poor quality DisplayPort cables in the past. I now only buy ones I know are brand name.