I tried that too, with no results.

However using advanced debugging techniques I found something new. I
added 3 prints in the finally, one before serv.server_close(), one
after, and the last at the end, after evt.set().
The first two works, the third one sometimes doesn't (i.e. nothing is
printed), even if no errors are displayed.

I'm not 100% sure but at some point I think I saw the third message
being printed at the beginning, before the first. But now I can't
reproduce it anymore.