I had a similar problem with my last monitor (with a Windows PC.) It would randomly flicker vertical lines, and those lines would show a “ghost image” of something that was on screen when it started. I think it had to do with its variable refresh rate, as it often seemed to happen after gaming or tabbing from full screen to the desktop. But I could never find a reliable way to replicate the bug.

I could always temporarily fix it by running a “stuck pixel” video in full screen for 10-15 mins, like this: (seizure warning) https://youtu.be/-2eQhhMvi-U

It wasn’t really “stuck pixels” but it seemed to blast the problem away for some reason. Could’ve been coincidence though.

If it’s a variable refresh rate issue between the Mac and monitor, you could also try turning Adaptive Sync off if you don’t need it: https://support.apple.com/en-us/102144 And also disable it in your monitor’s onboard settings if you do turn it off or already have it off.

I went through a few different GPUs over the years with that same buggy monitor, including the GPU I have now. I since upgraded to a new monitor, and this one has not had any problems in the 6+ months of using.

So I’d hazard a guess that it’s the monitor. Try the pixel video if it happens again or messing with Adaptive Sync. If it doesn’t work, try other similar videos. Maybe it will help.

I have an M3 Max that does this, but only when I plug in two monitors at once over Thunderbolt. It doesn’t always happen either, haven’t figured out exactly what is causing it. I know my M1 is only capable of a single external monitor, so part of my suspects their multi monitor support is just poorly implemented over the latest TB spec.

Using M1 with a thunderbolt dock doesn’t do it, so I know it’s not the monitor. Plus switching out one monitor for another doesn’t fix it.

In the past to debug this problem I’ve used BetterDisplay

Don’t want to send up a flare unnecessarily, but I used to see that patterning on machines with dead logic boards.

My last 17” MBP did that shortly before the board died completely & left me s.o.l. If you’re still under warranty or AC, maybe worth getting it checked?

I am not certain if this would be an issue with M-Series machines. If anyone knows for sure, I’d appreciate any info.

What is your resolution and refresh rate set to? MacOS can be quite picky.

Mine so far has had no issues like this. I have one monitor connected straight into the HDMI port and another monitor via a Dell dock (from work).