iMac 27 inch 2020 - Screen Glitch (Random Lines Appear on Screen)

Here we go problem sorted.

https://www.macworld.com/article/3583568/macos-catalina-10-15-7-update-is-now-available.html

Just update the OS.

Same issue with the white line here on macOS 10.15.6 with my AMD Radeon 5700XT 16GB Ram.

Not noticed it on Windows 10 yet.

SMC & NVRAM-Reset didn't help. Issue persists.

Also stressed the mac but it did not affect the issue. Seems to happen without any special impact.

Have one panic-shutdown-cause but I think this one was software-related.

Looking forward!

Greetings

Martin

For those of you with the glitch problem (most users in here I guess) who also plays GFX heavy to semi-heavy games - can you test to see if your experience a system wide crash like me and some others do after 10-15 min. of full screen play? I wonder if it's a heat issue.

I'm having the same exact issue with the horizontal white line flickering on the screen from time to time. I called Apple Support and reported the issue but of course, it was kind of useless. I seriously don't know what to do... return the machine and get another one or wait for a software patch, I mean... this is a real issue!

I don't know if my other problem with the same iMac is only for me and a few others in this thread, but playing a video game like Civilization VI for 10-15 min. in full screen is a sure way to make my iMac crash entirely with dramatic graphical glitches - only a hard reboot can save it each time. It happens every single time after max. 15 min. of gameplay so if you got yourself a game from Steam or so give it a try.

I have this issue too - I've had the iMac for 13 days and need to make a return decision ASAP. I have spoken to Apple support, been through the usual SMC, NVRAM rests etc. but the random line is still appearing once or 2 or 3 times an hour. I can't provoke it with a stress test or anything else.

Hoping it is a driver/software issue. Very disappointing for a very expensive machine.

Just as a reference point, there was a not totally dissimilar issue with the higher-end graphics option (of two) with the mid-2011, 27-inch iMac (iMac 12,2). The AMD Radeon HD 6970M with either 1 Gbyte or 2 Gbyte of memory developed on-screen lines, tearing, and (iirc) sometimes simply freezing. Many owners, myself included, had to haul their machines to Apple Stores or certified repair techs and wait for the swap to be made under AppleCare.

Two years after the machines were released, Apple finally instituted a free graphics card replacement policy up to three years after the machine was purchased.

Take a look at Activity Monitor and say again whether you think "literally nothing is running" when you don't see any user-facing apps with windows. On a modern OS, there are literally dozens of processes running in background. They may not be chewing up CPU or memory at any given time, but something is, even if it's only the logging services

I'm on my second iMac 27 inch 2020. The first one was shutting down intermittently an also had the glitch line appearing as well. I returned it it for an exchange which I received less than a week ago, and this one also has the glitch line that appears without warning. It flickers several times and then goes away and continues to happen. The still is from a video I capture with my phone while I was migrating while setting it up for the first time. This continues to happen to this day no matter what I am doing on the computer.

Apple has reached out to some of us for gathering information so they are looking into it, but I wouldn't expect them to come out and announce whenever/whatever the specific has been fixed whenever that situation might arise. The hardware concerns are what made me return my unit.

Having the same issue on my 2020 with 5700XT 16GB. White lines randomly glitch or flash, and corners of certain windows randomly fill in the rounded edge with blank pixels. The problem only appears to happen when the display is on the default resolution.

Specs: 27" iMac 2020, 3.8GHz i7, 64GB RAM, 1TB SSD, 5700XT GPU

Exactly the same issue for me! I can confirm the issue persists after starting in and out of Safe Mode, resetting the PRAM/NVRAM and SMC. It also happened whilst using 8GB RAM, 64GB RAM and a combined 72GB RAM (I believe this combination of different RAM sizes puts the system into single channel mode). Because the issue is a random white horizontal line flicker it is a lot less noticeable if you switch from Dark Mode to Light Mode, but still still happens nonetheless and is extra noticeable in programs like Final Cut Pro X which has a "dark" design by default.

I'm sure we'll all be watching for an update asap, because this issue is driving me crazy and the Mac will have to go back if there isn't going to be a software fix!

That will not help. I had 4x32GB before I returned my unit and I had the same issue. I'm pretty sure that it is purely a problem with the XT GFX, but whether it is a software or hardware issue (or both) still appears unknown. We can only hope that those of you keeping the unit can report the issue fixed by a software update.

Do let us know how it goes when you start to max out the graphics settings of your game. I checked it out on YouTube and it looks like a game that should demand more GFX than Civilization VI. If you can manage to max out your game and still run stable, we should be good overall.

I had one experience like that a couple of days after receiving the machine (~ October 19), but not since. I've been keeping up to date with OS patches; don't know if it had anything to do with that. I use TG Pro, but currently only with the default settings, which are set to spin the fans all the way up (~ 2700 rpm) when the average CPU speed hits 50 C. May tune that as time goes on.