2020 iMac Screen Glitch on Shutdown

Since replacement of Main Board the screen glitch has never come back. So I assume it is hardware related. See my earlier post in this thread

Hi everyone - thought I'd chip in on this. To me this is an OS issue and not hardware related. It would be unreasonable firstly to think we all have faulty graphics cards although of course, that's not impossible.

This glitch happens for me on my new iMac on shutdown as described by everyone in this thread. Out of curiosity, I reinstalled Catalina and I cannot get this glitch to replicate with that OS so that (I'm no techie) suggests to me it's software related.

it would be nice if Apple could acknowledge and release a fix for this as it's more annoying than anything else. I don't like buggy software.

Anyway, just wanted to report what I had found testing this out.

Has to be software related. We all can’t have dodgy hardware and I now can’t replicate the glitch on Catalina which I’ve reverted to.

I have actually rolled back to Catalina 10.15.7 where the shutdown glitch isn't replicated as it was annoying me no end and I won't update to Big Sur again until this, and other issues which are not being corrected are resolved (Bluetooth causing typing lag is another one that really needs looked at). Come on Apple at least acknowledge this Big Sur shut down issue is ACTUALLY an issue and what you intend to do about it....... PLEASE.

GusMcC, You'll have to let the rest of us know if you end up having the same issue. I ended up returning mine and repurchased one with the lower end graphics card. What a darn shame. I'll let everyone know if I experience the same issue with the lower end card. It comes in a couple days. As I mentioned in one of my earlier posts, I could make it occur anytime I let the screen go to sleep and then awaking the computer and then shutting down.

FZ

This issue wasn't addressed in the most recent BigSur update but as I have posted elsewehere, I have been told by Apple support this is a software issue, they are aware of it (now), and it will be addressed in the near future. It's annoying more than anything else and of course, shouldn't happen, but I think we just need to be patient a little longer. By the way, I rolled back to Catalina some time ago, as it annoyed me intensely (annoyed nothing else....) and I cannot get this glitch to replicate under Catalina.

Ava_Jt, thanks for adding your info to this thread.

You mention that you have a "change of color when entering my desktop." This might be normal behavior caused by the True Tone feature, which adapts the display to keep colors consistent under various lighting conditions. To check, go to System Prefs --> Displays and deselect True Tone. Try restarting with True Tone off; then with it on again. See if that makes a difference.

Mike

i agree on GusMcC response. Still... it might be a hardware thing which only appears on BigSur ofcourse... But as you say... i also roled back to Catalina and don't experience any issues which, to my believe, indeed shows it's the iOs.

I have the same problem. I have a brand new Mac with Intel Core i7, AMD Radeon Pro 5500 XT 8 GB and with the latest OS (macOS Big Sur version 11.2.3). The problem accurs during shutdown but only if my computer first goes to the sleep mode.

I have already replaced the screen with a new one but it didn't solved the problem. Apple says that it's probabley a software issue.

I have also a flickering screen issue when I log on to the computer and a change of color when entering my desktop. Hopefully Apple will solve these issues with the new update.

@P3-Mac

Thanks for writing this down! Its EXACT the same issue I have. And exact this:

" But as soon as the Mac is working over say 15 mins, the glitch is evident on each subsequent shut down. "

I also tried everything possible to figure this out. I also have iMac 2020, 10-core 5700XT 16GB.

Apple could you response or solve this issue ? There seems to be an error on the high end of the iMac. We need a good working and solid shutdown, I can't wait for this shutdown stall every time, it just doesn't make sense.

Guys, just to let you know that after I sent the computer to customer assistance the problem appeared again. Btw they told me that their specific diagnosis system didn't find any hardware issue, so, the only thing that they can associate to it is Big Sur bug. They just told me to stay relaxed about it and for sure it will go away with the next updates. Fingers crossed

Hi GusMcC, same here... back to Catalina no issues anymore. But you say the finally know about it (well well well.... that didn't took long).... so they pointed it to a software issue/bug in the iOS?

I have version 11.2.2, the latest update to date. I have the same problem here when restarting and shutting down. Called Apple today, shared my screen with them for them to look at, but still couldn't figure it out. So they scheduled me an appointment at the Genius Bar for tomorrow. But I'm not sure if I should bother unplugging all the cables, packing it in the box, unpacking it at Apple, packing it back in the box again, unpacking it at home, and finally plugging all cables back in only to be told that it is a software issue and that they would hopefully fix it with the new update.

Wauw FrankZ, let me reply on this that i have the 5500 XT card as well but i do have the issue as you can read in all my previous comments.

So, you now have a new computer and you don't experience the issue at shutdown? Now it is becoming really strange cause that would mean it might have something todo with faulty hardware.

And perhaps on the whole range of videocards used in iMacs.... as well as Macbooks... the AMD Radeons that is.....

In combination with Big Sur. Which could be a real possibility if Big Sur has a different usage of the videocard the Catalina has.

So it seems to appear on some of the videocards of some people so perhaps a whole line of Radeon cards just have this issue....

Which would mean if we would change the videocard the issue should be gone... is there someone who already has tried/done that with any feedback on this?

I can't believe people are actually returning their Macs because of a glitch on shutdown. Even if it were a hardware glitch - which is actually proven it is not because the issue does not appear on Catalina - who cares about the shutdown during the shutdown process? The 27" iMac screen technically consists of two screens which are placed next to each other. I'd bet the glitch is most likely due to a true tone command not sent to both screens during shut down. There is one claim in this thread that the split happend during normal operation, but not proven with screenshots or the like.