I can confirm that I have this same bug in both test and live environments. Clicking the “File URL” button allows the file to be added.
I think the problem is your metabox library. Currently the plugin uses this one: https://github.com/WebDevStudios/Custom-Metaboxes-and-Fields-for-WordPress in sermon-manager-for-wordpress/includes/meta-box/ which is no longer supported and probably needs to be updated to CMB2: https://github.com/WebDevStudios/CMB2
