There are several issues with the compatibility between WordPress’ built-in MediaElement script and the way this theme used to handle videos. The theme used to come bundled with the MediaElement script before it was included into core and have its own implementation. We’re probably have to rethink that entire implementation as WordPress’ implementation does not appear to support dynamic loading. This will take a while so you’ll probably want to roll back to an older version of WordPress or switch the theme until the issue is resolved.