@mrjj Thank you very much for your help! So show window, and then create a widget ... So still the question, it is a bug Qt or something else? The problem can be considered solved only in the bug tracker you need to add ...
@mrjj Hello, another mament noticed everything was decided widget loading after displaying the window, but if you minimize the window and deploy the freeze button again ...
I faced a similar problem, tried hacks with single QTimer and showEvent: timer was a solution, and showEvent -- wasn't. I also use Win10, but Qt5.5.1. Have you succeeded?