This is actually going to be fixed in an update coming soon. The reason you’re seeing a white background is because of the code in the “.entry“. If you look at other parts of your site that use “.entry” (the blog for example) it should have a white background. When you add a featured image inside of the footer widgets area, it’s just using that white background.
To fix it, you can remove it by adding this in your css –
.footer-widgets .entry {
background: none;
}