I'm on Windows 10. I have restarted the system and Zotero. I have changed the shortcut key from default in preferences and it still doesn't work. I have Zutillo installed and tried a shortcut there to focus the Collections pane (same as Libraries) and that doesn't work either. I think it stopped working on one of the latest Zotero updates.
It's possible that something else on your system is intercepting the shortcut.
Have you tried restarting?
I don't think it logs anything when I click Ctrl + Shift +L.