How can I remove filters from custom post types?

Try re-adding the ‘do_shortcode’ filter like so:

function landingpage_remove_plugin_filters() {

    global $wp_filter;
    global $wp;
    if ($wp->query_vars["post_type"] == 'landingpage') {
        remove_all_filters('the_content', 'plugin_filters');
        add_filter('the_content', 'do_shortcode');
    }
}   

add_action('wp','landingpage_remove_plugin_filters');