If you have lazyload installed on your website, you may have an issue loading the image for the widget, well it's easy to solve.
All you need to do is add the following to the end of the iframe embed code!
So it will look like
<iframe class="uvembed25646" frameborder="0" src="https://static.upviral.com/loader.html" data-no-lazy="1"></iframe>
This will allow the image in the widget to override the wits lazyload settings, without any change to your website.