I would like to confirm that I am seeing a similar bug with Qt programs. In my case I am not using Okular or Texworks, but Qt Creator exhibits this behavior when launching from the main menu, and my own custom Qt program also exhibits the behavior when launched from within Qt Creator itself and when launched from the file manager. As Alexei noted, it never occurs when launching from a terminal, and only intermittently occurs when launched from within the GUI. Qt Creator may open successfully some number of times and then the next time it hangs without showing a window and has to be killed from a terminal. I can't seem to find any logged messages indicating that something is going wrong.
I would like to confirm that I am seeing a similar bug with Qt programs. In my case I am not using Okular or Texworks, but Qt Creator exhibits this behavior when launching from the main menu, and my own custom Qt program also exhibits the behavior when launched from within Qt Creator itself and when launched from the file manager. As Alexei noted, it never occurs when launching from a terminal, and only intermittently occurs when launched from within the GUI. Qt Creator may open successfully some number of times and then the next time it hangs without showing a window and has to be killed from a terminal. I can't seem to find any logged messages indicating that something is going wrong.