Code Vision not working

I briefly saw a "2 usages" message in one project in my (Java) code earlier today, but that's the only example of "Code Vision" I've seen. It's enabled and everything is ticked, but nothing ever gets displayed. I quite often use the "Show Usages" menu option, so it's very appealing to have that available to me all the time via Code Vision. Do I have to do anything extra to trigger it or should it just work because the options are enabled?