Hello Mark,
I can see that you are using Jetpack plugin. The Jetpack plugin is the one responsible in putting up open graph tags (title, description, image, etc.) so that it will display correctly in social media posts.

Please be advised that Jetpack plugin will look for a featured image. The featured image will be used as the image to display when sharing the page or post in social media sites like Facebook and Twitter.
Please go to Pages > All Pages. Find your homepage and click “Edit”. When you are in the page editing screens, do not switch between editors. Simply find the “Featured Image” box on the right-side panel. The featured image will only appear if you are using the default page template. If you are using Blank - No Container page templates, the feature image will not display.
Hope this helps. Kindly let us know.