Querying Two Custom Post Types with OR Not Working

So the issue seemed to be with my second meta_query array – instead of checking if pub_date EXISTS, I decided to check if wpcf-date-time DOESNT EXIST:

$today = date( 'Y-m-d' );
        $args = array(
            'post_type'   => array('research_article', 'events'),
           'posts_per_page' => 10,
            'post_status' => 'publish',
            'orderby'     => 'meta_value date',
            'order'       => 'DESC',
            'meta_query' => array(
                array( 
                'key' => 'wpcf-date_time',
                'value' => $today,
                'compare' => '>=',
                'type' => 'DATE',
                ),
                array(
                  'key'      => 'wpcf-date_time',
                  'compare'  => 'NOT EXISTS'
                ),
                'relation' => 'OR',
            )
        );