$post not working any more?

I think the global $post doesn’t work any longer when using 5.0.3 and Classic Editor.

I have a custom function which stopped working after my update to 5.0, on 4.9.9 everything works great. I have installed Classic Editor as I have custom made plugins and themes that use this. I have a function which creates a serialized number when the post content is changed so that I can track this via javascript and automatically refresh the page if the content has changed.

If I create a post on 5.0 with the Classic Editor this function will no longer function. But if I edit a post which was created on 4.9.9 the function will work (with Classic Editor).

Here is the function:

function get_post_status_hash() {
    global $post;
    $data = array();
    $args = array(
        'post_type' => 'customposttype',
        'post_status' => 'publish',
        'orderby' => get_post_order(),
    );
    $the_query = new WP_Query($args);
    if ($the_query->have_posts()) : while ( $the_query->have_posts() ) : $the_query->the_post();
        if ( show_post_today( $post->ID ) && show_post_at_this_time( $post->ID ) ) {
            $data[] = $post->ID.":".$post->post_modified;
        }
    endwhile; endif;
    wp_reset_query();
    // Add theme settings
    $data[] = serialize( array(get_theme_mods(), get_widget_data_for_all_sidebars()) );
    return md5(implode(";", $data));
}