Message box before app launch

I’m trying to add a simple message box that will warn the user they have clicked an app to be launched in the launcher and that it dismisses as soon as all the bootstrap is completed and the app_launch is finally executed.

I’ve tried adding this to before_app_launch hook at the beginning of the execute method:

        # create and show the QMessageBox
        msg_box = QtGui.QMessageBox()
        msg_box.setText(f"Launching app \n{software_entity['code']}\n Please be patient.")
        # allow the main application event loop to continue running
        # while the QMessageBox is displayed

This will show the message box but it dismisses it as soon as it is created.
Adding a nasty sleep(2) delays the hole execution but at least shows the message box for 2 seconds.
The thing is that the first time you select a project and launch an app, the message box will never show, from the second time on launching any app, it will.
What am I doing wrong?