Elementor breaks site with custom shortcode

I created a custom shortcode which includes a special loop which includes all posts from different multisite blogs. This solution is provided by this plugin: https://rudrastyh.com/. The shortcode is perfectly working an all normal pages and posts.

But I am also using the page builder Elementor. When inserting this shortcode into Elementor some strage things are happening: in editor mode the shortcode output is showing up twice, once at the top of the editor area and once again at the place where I actually put the shortcode. When I hit save, my whole site breaks and shows a standard image when accesing any page. Then the the only solution is to recover my latest database backup.

Here my shortcode fuction:

// Add Shortcode
function all_events_shortcode ($atts) {

    // Attributes
    $atts = shortcode_atts(
        array(
            'lang' => '',
            'blog' => '',
        ),
        $atts
    );

        // Network_Query parameters
        $args = array(
            'posts_per_page' => 14,
            'blog_id' => esc_attr($atts ['blog']),
            'lang' => esc_attr($atts ['lang']),
            'orderby' => 'meta_value_num',
            'order' => 'ASC',
            'post_type' => 'noo_event',
            'meta_key'  => '_noo_event_start_date',
            'meta_value' => date( "U" ),
            'meta_compare' => '>'
        );

        $network_q = new Network_Query( $args );

        // if there are posts, then print <ul>
        if( $network_q->have_posts() ) :
            echo '<div id="all_events">';

            // run the loop
            while( $network_q->have_posts() ) : $network_q->the_post();

                // the get_permalink() function won't work without switch_to_blog()
                // you can use network_get_permalink() instead but it is a little slower
                switch_to_blog( $network_q->post->BLOG_ID );

        // Get the dates
        $start_date=get_post_meta($network_q->post->ID, '_noo_event_start_date', true);
        $_start_date = gmdate("d.m.Y", $start_date);

        $end_date=get_post_meta($network_q->post->ID, '_noo_event_end_date', true);
        $_end_date = gmdate("d.m.Y", $end_date);

                // you can obtain the post title from $network_q->post object
                echo '<div class="all_events_item post-' . $network_q->post->ID . ' blog-' . $network_q->post->BLOG_ID . '">
                    <div class="all_events_img">
                        <a href="' . get_permalink( $network_q->post->ID ) . '">
                            '.get_the_post_thumbnail( $network_q->post->ID, 'large' ).'
                        </a>
                    </div>

                    <div class="all_events_content">
                        <h2><a href="' . get_permalink( $network_q->post->ID ) . '">' . $network_q->post->post_title . '</a></h2>
                        <br />
                        <span class="start_date">'.$_start_date.'</span> - 
                        <span class="end_date">'.$_end_date.'</span>
                    </div>
                </div>';

                // restore_current_blog() to switch to the previous (!) website
                restore_current_blog();
            endwhile;

            echo '</div>';
        endif;
        network_reset_postdata(); // add it after the loop if you plan to use Network_Query multiple times on the page
}
add_shortcode('all-events', 'all_events_shortcode');

Can you give me some hints how I could tackle this problem?

Best wishes