To reproduce, try updating a macOS machine to the current Mojave preview build (macOS 10.14.4 Beta 18E215a), then try building and running one of the Qt Quick using example applications (I tested with the 'window' example).

In each case, the application launches, a window is created, the content is rendered, but then the application becomes unresponsive. If you attempt to resize the window, the content is then skewed according to the newly-sized window, rather than re-rendered.

This doesn't happen in the current macOS Mojave release (10.14.3) so hopefully this is just something that Apple will fix on their end, but figure it was worth making sure the Qt team was aware.

The issue also does not occur with Qt 5.9.7.

See also: QTCREATORBUG-22131