strange colored squares in the screen
Hi everyone, it has been a couple of weeks now since I have these strange colored squares that appear and flash on my iMac. I did a full NVRAM and SMC reset but the problem comes back. See the example in the attached image.
It seems that the problem comes more often when I open an app for the first time, especially Safari.
Anyone has ever seen something similar? I really don't know what to do...
Thanks!
macOS High Sierra (10.13)