Updated WordPress to latest version - Upfront throwing fatal error

I updated to the latest version of WordPress, and the Upfront theme is throwing a fatal error:

Fatal error: Class 'WP_Screen' not found in [path to wordpress removed]/wp-content/themes/upfront/elements/upfront-this-post/lib/this_post.php on line 539

Help! All plugins and themes are fully updated. If I can't get this sorted soon I will try to roll back...