Thanks for reply, my problem is different, the artifact appear on printing too, my macpro don't slow down. The video now is public, give me a feedback, thanks.
Mario, now I can see your video. I have already seen that bug from another person. Clipping to a group can also massively slow down PS in this current release or, like in your case, cause artifacts.
Stefan, do you have a file that exhibits the behavior in the video or the slowdown you're referencing? If so, that would be helpful for me to track down the issue and get it fixed.