I'm having the exact same problem and I resorted to a ugly hack of calling
before calling QT5_WRAP_UI
I don't know why but the value of Qt5Widgets_UIC_EXECUTABLE comes up as empty string (or unset)
I found the cause of those error, it is due to fonts.css in html files.
When I removed the link from <head>, the application was successfully run without crashed.
Just wonder, how come its not working now in qt5.8 but just nice back then in qt5.5 ?
BTW, thanks both for your help and idea :)
Ok. noted. I will start over and get back to you.
For now, it considers solved.
Thank you very much :)