Hi there,
the background image isn’t being lazyloaded – very few plugins provide lazy loading for CSS backgrounds, their generally a paid server side option.
The delay in it being displayed is because its a CSS Background image, the request for that image doesn’t get made until the sites CSS is loaded, whereas an <img>
element the request is made during the HTML loading stage.
With a custom background image there isn’t any easy way to improve its loading, without manually coding the CSS for each place your using the a custom background hero.