iMac 27" 5K Late 2015 screen artefacts on shutdown

A read through the posts on this topic will show that Apple are definitely looking into this problem.

Several of us have been contacted by Apple and have submitted reports and screenshots.

There is no need to change your iMac.

If this is a software problem, Why does it only seem to be happening on iMacs? Seems there maybe a known problem that Apple aren't letting us know about to avoid yet another secret recall by Apple. They seem to be swapping hardware as a solution.

I had the same issue on my Late 2015 27" 5K iMac that I purchased on November 2016. Since day one the screen would show Matrix green lines, sometimes Blue and Sometimes purple and white lines ONLY when I turn the machine off and NOT every time. I called Apple support and of course they were clueless so I had to carry the machine to the store to be fixed by the Apple 'Geniuses'. They couldn't find anything wrong during their in store diagnostics so they asked me to check it in for more advanced level diagnostics. Called me the second day and told me they can't find anything and asked if I can email them the video of the issue that I took on my phone camera, so I did. They called back in 4 hours and said "It is probably the video card, we're going to have to replace the logic board" I refused to have my brand new computer opened so they replaced my iMac with a similar brand new one. took it home did all the recommended updates out of the box and guess what? Voila! problem is there again on the second brand new iMac which makes me think that it is either a software problem or a hardware issue on a mass number of their late 2015 iMac machines. Does anyone here get the same issue on their iMac that is NOT late 2015 5K 27"?

Wow the posts are certainly coming in now! My iMac was purchased in October 2015 and has this issue, if it were faulty hardware, which I hope isn't, Apple would have one huge recall on their hands! iMacs sold from then right up to present and even now being affected, would be one heck of a recall. Personally, and as I have said before, I believe this is software as only shows in Sierra - here's hoping!

Same problem here. Took delivery of my iMac 27" 5k January this year. First noticed something strange was going on with Logic Pro (unusable atm due to laggy GUI), then started noticing the weird glitches when I power my iMac off.

I have been in contact with support to inform them about the behaviours in case it turns out to be a hardware problem.

My 27" iMac was delivered on Jan 24, 2017. This is my 2nd 27" iMac (returned one bought in Dec 2016)

I did the latest Sierra update two days ago.

It's still getting the wide, colored bands upon shutdown.

The software update did NOT help.
Today is Feb 5, 2017, and I am still getting the strange lines on a brand new iMac.

Apple is trying to work on it. I, too, have been contacted by Apple.

I'm seeing the problem (intermittently) with the standard video card for this computer, AMD Radeon R9 M395 with 2GB video memory. Is anyone seeing it with the upgrade, AMD Radeon R9 M395X with 4GB video memory?

I'm on my second (2nd) 27 inch retina iMac in a little over a month. Returned the first one and reordered a

replacement. Different video cards on each one, both special order builds with ssd drives. Both have the same issues on shut down with random weird screen artifacts.

I'm NOT a happy Mac user at this point! Back to the local Apple Store genus bar to see what they say this time.

Hi, Apple have been aware of this problem since the beta version of Sierra, then i went back to El Capitan after my iMac was showing the problem... So when the full version of Sierra was released i updated to it. Apple first tried to say wait for updates back in September.. so i did and the updates didn't resolve the problems.. so apple sent my 1st iMac 5k 27inch 1tb fusion drive And Radeon M390 2048mb off for repair they replaced the Screen HHD and logic board .. with no joy the problems still there back in October last year. Then respectfully they replaced my machine with one built in September of 2016. My iMac is unstable when running sierra

I have been speaking to a friend and we are able to take a class action against Apple..So they will have to start explaining when they are going to fix this problem or not so we are not left with iMacs what show signs of issues. as all what apple is telling people is to wait for updates which don't resolve the problem .. i have upgraded and downgraded every time when there is new update ..

I have spoken to apple today and they say the same thing, as i said (( this is like buying new microsoft laptop windows 10 and it only able to run windows 8.1 .. Apple do not know what is going on with these 5k iMacs so more people listen to them and getting throbbed off, less likely they will do anything ...

Just in case anyone might think this is being fixed in the latest beta, the priority is apparently: "dictation support for Shanghainese & cricket scores" which of course one can understand the overwhelming need for rather that fixing video glitches.

I have the issue ,too.

"horizontal or vertical lines appearing in Time Machine"

- and also a black rectangle in the Finder window. Very scary!

How could apple deliver such a product with this huge problem by its own software and hardware???

2/8/17 update. After two logic board replacements, it did it again on restarting the iMac this morning. Here, I thought it was fixed because it seemed fine for over two weeks since the second repair. Hoping Apple gets there act together soon. This is something I'd expect from a Windows machine, not a Mac.......

I agree. I have had this computer for over a year and 3 months, and all started when I updated to Sierra. I am hoping that someone out there is listening. Occasionally my wired mac keyboard also loses connection. I have unplug, and plug back in. Weird things a foot.

I don't understand why some people are going backwards and forwards to get hardware service on their Mac when this clearly must be a firmware or driver issue if it only happens to occur in macOS Sierra but not in OS X El Capitan. No amount of logic board or display assembly replacements are going to help until Apple provides a software update to address the problem.

I understand Apple is responsible for causing the problem and is certainly a poor demonstration of quality, but if it doesn't affect your use of the machine until you shut down your Mac, I'm struggling to understand why people find this issue so significant. Do these artifacts occur in the middle of using the machine?

Whilst I agree its a software issue and a waste of time sending the mac to be serviced, I'm glad people are doing this; the more that do, the sooner Apple might notice the rising cost of repairs and fix this problem.

The issue isn't significant in and of itself but what is significant is the length of time Apple has left this unresolved. Its a clear demonstration how macOS has been downgraded in favor of iOS.