Hi,

If I understand you correctly the breadcrumb doesn't display the repeat offset?

If that's the case then try following: 

In your active theme functions.php file add this filter:

add_filter('rank_math/frontend/breadcrumb/html', function($html, $crumbs, $th) {
    global $post;
    if ($post && $post->post_type === 'stec_event') {
        $repeat_offset = get_query_var('stec_repeat_offset');
        if ($repeat_offset) {
            $arr_html    = [];
            $crumbs_html = [];
            $arr_html[]  = '<nav aria-label="breadcrumbs" class="rank-math-breadcrumb"><p>';
            $event = new \Stachethemes\Stec\Event_Post(get_the_ID());
            $event->set_repeat_offset($repeat_offset);
            $separator = \RankMath\Helper::get_settings('general.breadcrumbs_separator');
            foreach ($crumbs as $crumb) {
                $crumbs_html[] = sprintf('<a href="%s">%s</a>', $crumb[1], $crumb[0]);
                if (!next($crumbs)) {
                    $crumbs_html[] = sprintf('<span class="last">%s</span>', $event->get_start_date('Y-m-d'));
                }
            }
            $arr_html[] = implode('<span class="separator"> ' . $separator . ' </span>', $crumbs_html);
            $arr_html[] = '</p></nav>';
            $html = implode('', $arr_html);
        }
    }
    return $html;
}, 10, 3);

This filter will add the recurrence date at the end of the breadcrumb if there is one.

I'll add to my todo list to edit the authors list alphabetically.