Hi there Simon!
My apologies for not replying earlier, the notification got lost in my backlog.
The theme is outputting an empty description field at the top of your page’s header:
<meta name="description" content="" /> <meta name="keywords" content="music photography magazine" />
I advise looking into removing that via the theme options. I also recommend removing the meta keywords, as they have adverse effects.
I think you can easily flick the “SEO” switch in your theme, and the problems should go away. Please note that Google needs to crawl your pages again to discover this change.
I also recommend signing up for Google’s Search Console to manage your website’s presence in Google. You can validate the Search Console’s meta tag in the SEO settings, within the Webmaster’s meta box.
The console warns you on issues early, so you won’t have to crawl the search engine.
If you wish for me to verify your changes, feel free to ask!