Qt for Python (PySide/Shiboken)

I see you've provided a minimal reproducing example. That's generally the first thing I suggest to people not getting traction / attention on a bug from devs. However this one I see involves very particular environment setup (xfce or openbox window manager). I guess the next thing I'd suggest is to see if you can provide a docker image (can you have window manager running in a docker container? I'm pretty sure, but don't think I've ever seen it), or a VM that has the environment all baked in, so the bug is easy to reproduce. Since you say it can take minutes or many hours to reproduce, try to automate the reproduction process, so you can start the app, let it run until the bug occurs without human user input. Better would be to see if you can make the problem show itself in seconds, but that may not be possible.