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

I'd return it.

Random white line is corrected with Catalina 10.15.7 . But corner glitch still there.

It was fixed with latest update. Haven’t had issues since updating, corner glitch gone.

Ok... I have like zero of these issues. It sounds like something is seriously broken on your machine. Would not be satisfied either and would ask for a replacement ASAP

Common advice for any iMac especially...

Have you blown the dust out of the intakes lately?

What temperatures does this App report? Especially the GPU.

This App can be used to speed up the fans, all my iMacs would be dead without it.

Never ever ever drop fan speeds below the speed that the Mac itself is calling for.

MacFansControl…

https://www.crystalidea.com/macs-fan-control

I have had worse issues with 2020 27" with 5300

Has been returned and replaced.

Hey folks,

got the same issue as mentioned by the OP. White horizontal white line flickering / flashing. First time I've seen it was right during setting up, however, thought my eyes were just playing tricks on me. After that I noticed it on the desktop without running anything besides finder of course.

While using Adobe Bridge it happened more frequently (skipping through fullscreen previews of RAWs). Resetting the NVRAM didn't help nor made pushing the iMac to its limits the glitch / issue worse. It just happens now and then. My OCD says I should request for a replacement ASAP especially considering the price tag ;D

iMac 20,2 27" 3,8 Ghz 8 Core i7 + 5700 XT.

Exactly the same. Hard reboots and graphics artefacts. Was after playing city skylines. We tried apple support but would have been stuck with out devices for up to 4 weeks. So we returned it to place of purchase.

To clarify, in case I made things perfectly obscure: Apple was replacing 2011 iMacs with the issue well before August, 2013 under AppleCare (and, iirc, after the first 90 days after pour case, out of the "goodness" of their hearts). It was only in August, 2013 that that service notice leaked (or was purposely leaked; trying to read Apple is often like trying to read the pre-1989 Kremlin). I wish I could remember the month and year when mine got replaced, but I can't. I have a vague idea that the issue didn't develop for me on day one (early November, 2011), but waited until the following spring sometime to rear its ugly whatever — possibly thermal?

A little more Intertubes searching turned up tales of being able to cure (literally) the 2011 model issue. But the 2020 model issue appears from the git-go in some people's machines, so please don't take your still-under-warranty machines apart just yet.

From my experience dealing with Apple over ~ 30 years, they do see statistics on reasons for AppleCare calls, and they will deal with this, but it's unrealistic to expect an engineering change in a few weeks. (They have to reproduce the issue in machines coming off the assembly line, do a bunch more of that to get an idea of the prevalence, troubleshoot to discover the root cause, and then implement a solution, which could turn out to be hardware or software). Seems like most people here realize that, and are either bringing recently purchased machines back during return periods, or holding off ordering this CTO option until a fix has been devised, both of which make perfect sense.

[Edited by Moderator]

I just want to let everyone know that I have not seen any lines since I first configured my iMac and they were not as severe as the photos I have seen, they were very brief and very thin. Also I do hear the fan when doing non-intensive tasks but it is very quiet. I don't think this should put anyone off of purchasing. Just exchange it if it has crashing/lines or any other issue.

Where are you? There a lots of Apple Stores currently open at least as "storefronts" (pick up and, don't know, maybe drop-off, too?) in the US: https://appleinsider.com/articles/20/05/25/heres-where-apple-stores-have-reopened-around-the-world.

Apple tends pretty much never to admit in, say, a press release that there's hardware flaw, even after they've diagnosed it and have a free repair program. At some point, that information just becomes available through AppleCare and the Genius Bars — and this the net. If it's a software issue, that'll probably get mixed into "an upcoming release" of the OS. 11.1? We can hope.

It Does, I noticed in Dark mode it was easier for the glitch to catch the eye. However, I also noticed that the glitch in dark mode sometimes came across as a lighter gray color (but still was more noticeable). In non dark mode it was a whitish glitch for me, in Dark mode (Well not the first unit) was more a bright gray, The Second unit it would by a near white or a bright white... I have since sent them both back and hoping they figure it all out.

For some users they appear every half an hour, for others only a couple of times a day and for some only once in a few days.

@aaronshort have you got a second screen attached by any chance?

Are you by any chance a gamer who could load up a demanding game to see if the system survives or crashes after 10-15 minutes of playtime?

I'm fairly sure the issue is solely with the 5700XT graphics itself irrespective of the CPU (8-core vs 10-core) configuration. But please report back if the glitching starts happening!