Steps:
Build and run the example application
Press "Open message"

Result:
-Message dialog text is blurry
-You cannot press either one of the buttons
-You get an error setGeometry: Attempt to set a size (248x87) violating the constraints(248x118 - 16777215x16777215) on window QQuickWindow/''.
-Message dialog layout seems to be uncorrect

Close the message dialog and press "Open message" again, after that you're able to press the buttons and the error is gone but the rest of the problems are still there.

Everything works fine if you use QApplication instead of QGuiApplication