It's kind of ironic, but I've the exact opposite problem in linux mint, just installed the xfce version and when I type in my password it sometimes does not unlock, the screen kind of hangs with a spinning icon. I can recover by starting a console session (ctrl-alt-F2) and killing the screen saver session thst way and then returning to the GUI. Other than this annoyance, my laptop is running really nicely on Linux mint, a Ed a creaking old Windows laptop from the bin.

How does this kind of vulnerability even remain, after code reviews?

Is it hard to spot?