Recently I found that xubuntu on my laptop would not show me the desktop after waking up.
Second or third try it would work. But it seems this is a known problem and the solution is to uninstall lightlocker and install xscreensaver.
So somebody broke lightlocker and now its almost useless. It doesn’t get fixed and it doesn’t get removed as the default screen lock handler, you just end up with a laptop that won’t reliably wake up.