Wordpress - Why is "/page/2/" not working?

Found the answer:

After a looong day debugging thru wordpress core, I managed to solve this issue.

Basicly, you CANT have a PAGE and a CUSTOM POST TYPE with the same name. If you do, the permalink rewrite rules will get confused and trigger a 404.

A very simple solution I'm using is: The page that lists the custom post types is called in plural (eg. products) and the actual post type name is in singular (eg. product). So they dont conflict and it's all fine.

Done Done! Hope this will save people's time.

• via rafaelxy (http://wordpress.org/support/topic/pagination-with-custom-post-type-listing)

After a long time I found a solution for this issue (thanks to franzblog).

If you are using version 4.2 or higher, you need to add the following lines in your functions.php file:

add_filter( 'redirect_canonical', 'custom_disable_redirect_canonical' );
function custom_disable_redirect_canonical( $redirect_url ) {
    if ( is_paged() && is_singular() ) $redirect_url = false; 
    return $redirect_url; 
}

Everything is working fine now!

you CANT have a PAGE and a CUSTOM POST TYPE with the same name

Maybe tree years ago it was impossible, but now you CAN.

First, add this lines to $args into your post type:

'has_archive' => false,
'rewrite'     => array(
                 'slug'       => 'your slug', // if you need slug
                 'with_front' => false,
                 ),

Second, in functions.php add action:

add_action('init', 'custom_rewrite_basic');
function custom_rewrite_basic() {
    global $wp_post_types;
    foreach ($wp_post_types as $wp_post_type) {
        if ($wp_post_type->_builtin) continue;
        if (!$wp_post_type->has_archive && isset($wp_post_type->rewrite) && isset($wp_post_type->rewrite['with_front']) && !$wp_post_type->rewrite['with_front']) {
            $slug = (isset($wp_post_type->rewrite['slug']) ? $wp_post_type->rewrite['slug'] : $wp_post_type->name);
            $page = get_page_by_slug($slug);
            if ($page) add_rewrite_rule('^' .$slug .'/page/([0-9]+)/?', 'index.php?page_id=' .$page->ID .'&paged=$matches[1]', 'top');
        }
    }
}

function get_page_by_slug($page_slug, $output = OBJECT, $post_type = 'page' ) {
    global $wpdb;

    $page = $wpdb->get_var( $wpdb->prepare( "SELECT ID FROM $wpdb->posts WHERE post_name = %s AND post_type= %s AND post_status = 'publish'", $page_slug, $post_type ) );

    return ($page ? get_post($page, $output) : NULL);
}

Don't forget to flush rules in dashboard.