Blank Page in Envato OneVideo Theme

Did everything required and read all support forum posts. I can see my 404 page in review but when tested in the plugin admin’s “Test 404 Error” it does not show the custom 404 page. Just my theme header and footer and template but not the 404 page inside. I am using Envato/Themeforest OneVideo theme. I tested with WP TwentySixteen and I can see the error page. So how do I make this work with my theme? Thanks