I noticed that projects that I compile on Xcode 9 (beta then, release now) have all a strange behavior. When a view scrolls behind the title bar (either with toolbar or not) the blur/translucency fails to update as quick as the scroll occurs and it results on artifacts appearing.
It looks like this :
You can notice how the blue highlight from the selected table view cell left a mark on the title bar blur.
Same here but it is just a portion of the bar.
I also made a video so anyone can see it live.
I tried to compile the same test project on 2 different machines but the result is the same. One of the machines is running up on a fresh install. Both are macOS 10.13/Xcode 9.0
This test project is available on GitHub.
Does anyone have an idea on what is happening ? If not I'll file a radar.