Parent Category link to its sub categories on different page

I think the simplest way would be to just use the category archives that WordPress already generates. Change the category base in permalink settings to issues so you have nice URLs, then in the category template, check if you’re viewing a top level or child category, and display the appropriate markup:

$this_category = get_queried_object();

// if parent is 0, category is top level
if( 0 == $this_category->parent ) :

    // top level category,
    // show child categories of this issue
    $args = array(
        'child_of' => $this_category->term_id,
        'title_li' => '',
        'hide_empty' => 0
    );

    // output a list of child cats for this issue
    // see also get_categories or get_terms if you wish to use your own markup
    wp_list_categories( $args );

else :

    // child category,
    // show articles in this subcategory, etc.
    echo 'child category';

endif;