The plugin is currently disabled because I’m relying on some custom module I created to fix the VC lazy loading on the server side.
I don’t think you need a sample to tell you the issue, though. Lazy loads generally work by outputting the data-src on the server side, and transforming that to a background-url on the client side. Your plugin does both the transformation to data-src and back to background-url on the client side. Because you’re never sure when javascript is executed, the browser may already be loading the images when your script triggers.
Also note that (1) VC outputs styles in-page, so they are available at page load time and (2) your plugin scripts might be loaded after that because of WordPress optimizations