Regarding the freezing, maybe it helps to change "hog mode"?
Regarding retina issues, can you try to change
<key>NSHighResolutionCapable</key>
<true/>
to
<key>NSHighResolutionCapable</key>
<false/>
in Radium.app/Contents/Info.plist ?
Besides this, I don't have any suggestions yet. Developing for macOS is hard since each new version of the operating system introduces new problems, plus that macOS in general behaves differently than windows and linux. I tried updating all system libraries and Qt in 5.4.0, but I got crashes in 10.13 after doing so (which I didn't get before), so it probably didn't help. I think the source of the graphical problems has got something to do with OpenGL, and OpenGL doesn't seem stable on macOS at the moment, at least I read of others struggling with opengl as well. Anyway, it might help to use 5.3.3.