Thanks for using the Yoast SEO plugin. I can confirm that your featured image isn’t shown in mobile search results. The plugin outputs a property called primaryImageofPage in the page’s schema data, a reference-by-ID to a node representing the page’s featured image.
However, whether Google displays the image in the search results is entirely up to Google. Apart from the schema markup for the primaryImage in the schema data, there are other factors (i.e., authority, context, etc.) that Google may take into account to decide whether or not to display an image next to your pages.