What causes artifacts on the iMac 27 late 2015 monitor?

Question

Video cards

I bought a new iMac the other day in mvideo.
iMac (Retina 5K, 27-inch, Late 2015)
AMD Radeon R9 M390 2048 MB
3.2 GHz Intel Core i5
Everything seems to work fine (well, photoshop slows down) except for one thing. At the end of the session or shutdown, artifacts appear in the entire monitor. Bright colored stripes. Not for long, about 5 seconds.
What is the reason for this and what should I do? Of course, you can take it for repair or take it to the store (14 days for verification), but for example, the rag from the kit has already been taken out of the package and the apple sticker alone has already been used))

Answer 1

On the support forums, many people ask a question, they promise to fix it in the next big update. I manage to remove it by resetting the PR memory (I don’t remember exactly what it’s called correctly), but there are not so many combinations. All this is not critical.