I almost went mad over background images.
I’m developing a new website on a local server: http://127.0.0.1/mw/
When I load a custom background image on a h2 element. It does nothing.
It took me a while to figure it out, but in order to make it visible in a localhost enviroment I had to get rid of the first “/” (dash). I should point out that the first dash is added by the plugin by default.
It’s not really a bug, it’s a quirk of your setup. You are using a sub-folder for WordPress, but the root for relative paths is still set to the root folder, rather than your sub-folder. You can solve this be entering absolute URLs instead e.g.