Taxonomy doesn’t follow slug permalink structure

There’s no such page in WordPress. /issues/ doesn’t exist. All WordPress URLs display either a single post/page, or a list of posts/pages (search, date archives, category archives etc.). So there’s no way WordPress will list terms. If you create a new issue, then that will be accessible at /issues/issue-name/, but nothing will exist on /issues/ by itself.

If you want to list all issues, then the simplest method would be to create a page called Issues, then create a custom page template that lists all terms in the Issues taxonomy. You can do this with get_terms():

$issues = get_terms( [ 'taxonomy' => 'issues' ] );

if ( ! is_wp_error( $issues ) && $issues ) {
    foreach( $issues as $issue ) {
        echo $issue->name; // Name of issue.
        echo get_term_link( $issue ); // URL to articles in that issue.