I compiled qt from source with vulkan including the examples. When you start the hellovulkan triangle then you can see the triangle rotating until the triangle frame freezes. The triangle appears stuck. When you resize the window, then the triangle can be seen rotating again. It periodically freezes again. 

This happens to all QVulkanWindows. There is also reports from other users: https://forum.qt.io/topic/160556/qvulkanwindow-freezes-until-window-resize-on-macos-only
(qtbase/examples/vulkan/hellovulkanwidget/hellovulkanwidget.cpp)

I debugged the grapics pipeline with XCode and i can see that the graphics pipeline does not freezes, it produces the correct frame*. The Qt embedded vulkan frame however does not and freeze. I seems like the swapchain is presented to the surface but the surface is not updated.

*to debug the example app, use XCode, Debug->launch executable. In the options, select GPU Frame Capture as 'Metal'. Then launch the hellovulkan example trianlge app and in XCode, in the right panel, the bottom panel has a toolbar icon that is the Metal icon. Use that to capture the frame and you will see the vulkan graphicspipeline has the correct output frame (not frozen).