Get newest value of an array

It sounds to me like you want to get the most recent term from your issue_filter taxonomy. To do that you’d want to use get_terms() with a few arguments.

$t = get_terms(
  'issue_filter',
  array(
    'orderby' => 'id',
    'order' => 'DESC',
    'number' => 1,
    'fields' => 'ids'
  )
);

That should get you the most recently created term with content as an array of IDs. Your tax_query will accept that array as is, so…

$the_query = new WP_Query(
    array(
        'post_type'      => 'news',
        'posts_per_page' => '-1',
        'tax_query'      => array(
            array(
                'taxonomy' => 'issue_filter',
                'field'    => 'slug',
                'terms'    => $t
            )
        )
    )
);