python – The FBS (pyqt) application behaves strangely

I have a PyQt desktop application (FBS).
When I open it, everything works correctly first, but as soon as I do an action like clicking a button. The action supposed to occur does not appear on the screen.enter the description of the image here

After pressing next, the application is always the same.

But even if the application does not indicate the change in background, she does what she is supposed to do. (For example, in some cases, disable the next or previous button).
What worries me most is that if I change screens and go back to the application, everything looks as it should.
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Why is that? and what can I do to solve this problem?