tnoguchi on "Paginated Custom Post Type Archive: 404 Error"

I've been getting a 404 error on a CPT archive page, and am not sure why. I can go to the page set for the custom post type archive, but the next page /mycustomposttype/page/2 gets a 404 error.

I don't think that there's anything wrong with my code and I've flushed my permalink rules and I think that the CPT is registered correctly. But my code is below. Any insights would be greatly appreciated since I can't see why the pages are not being found.

<!-- Row for main content area -->
    <div class="full-width" role="main" >

     <section id="sketchbook-wall">

       <ul id="sketchbook-container" class="large-block-grid-4">
            <?php 

            $paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
            $args = array(
              'post_type' => 'tn_cstm_sketchbook',
              'orderby' => 'menu_order',
              'order' =>  'ASC',
              'posts_per_page' => 2,
              'paged'=> $paged
              );

              $loop = new WP_Query($args);
              while($loop->have_posts()) : $loop->the_post(); ?>
              <li>
                <figure class="sketch-thumb">

                <?php
                   if(get_field('sketch')) {
                    $sketch = get_field('sketch');
                    $large_image = wp_get_attachment_image_src( $sketch, 'full' );
                    $thumbnail = wp_get_attachment_image_src( $sketch, 'large' );
                    $attachment = get_post( get_field('sketch') );
                    $alt = get_post_meta($attachment->ID, '_wp_attachment_image_alt', true);
                  }
                ?>    

                <a href="<?php echo $large_image[0]; ?>" data-id="<?php the_ID(); ?>"  class="reveal" >

                  <img src="<?php echo $thumbnail[0]; ?>" alt="<?php echo $alt; ?>" />

                </a>
                <figcaption>

                </figcaption>

                </figure>

              </li>

            <?php endwhile; ?>

          </ul>

      <nav>
        <?php
        // Bring $wp_query into the scope of the function
        global $wp_query;

        // Backup the original property value
        $backup_page_total = $wp_query->max_num_pages;

        // Copy the custom query property to the $wp_query object
        $wp_query->max_num_pages = $loop->max_num_pages;
        ?>

        <!-- now show the paging links -->
        <div class="alignleft"><?php next_posts_link('Next Entries'); ?></div>
        <div class="alignright"><?php previous_posts_link('Previous Entries'); ?></div>

        <?php
        // Finally restore the $wp_query property to it's original value
        $wp_query->max_num_pages = $backup_page_total;
        ?>
      </nav>

     </section>

     </div>  <!-- End Content -->

    <?php

        // Register Custom Post Taxonomy
         public  function create_work_taxonomies() {
                register_taxonomy(
                    'tn_cstm_sketchbook_plugin',
                    'tn_cstm_sketchbook',
                    array(
                        'labels' => array(
                            'name' => 'Sketchbook Categories',
                            'add_new_item' => 'Add New Sketchbook Category',
                            'new_item_name' => "New Sketchbook Category"
                        ),
                        'show_ui' => true,
                        'show_in_nav_menus' => true,
                        'show_admin_column' => true, //Show custom taxonomy in admin columns
                        'show_tagcloud' => false,
                        'hierarchical' => true,
                        'args' => array( 'orderby' => 'term_order' ),
                        'rewrite' => array('slug' => 'sketchbook-categories', 'with_front' => false )
                    )
                );
            }

        // Register Custom Post Type
           public function create_sketchbook_work() {
                register_post_type( 'tn_cstm_sketchbook',
                    array(
                        'labels' => array(
                            'name' => 'Sketchbook',
                            'singular_name' => 'Sketchbook Page',
                            'add_new' => 'Add New Sketchbook Page',
                            'add_new_item' => 'Add New Sketchbook Page',
                            'edit' => 'Edit Sketchbook Page',
                            'edit_item' => 'Edit Sketchbook Page',
                            'new_item' => 'New Sketchbook Page',
                            'view' => 'View Sketchbook Page',
                            'view_item' => 'View Sketchbook Pages',
                            'search_items' => 'Search Sketchbook Pages',
                            'not_found' => 'No Sketchbook Pages found',
                            'not_found_in_trash' => 'No Sketchbook Pages Found in Trash',
                            'parent' => 'Parent Sketchbook Page'
                        ),

                        'public' => true,
                        'show_in_menu' => true,
                        'menu_position' => 29,
                        'taxonomies' => array( '' ),
                        'menu_icon' => plugins_url( 'images/sketchbook-icon.png', __FILE__ ),
                        'publicly_queryable' => true,
                        'query_var' => true,
                        'rewrite' => array( 'slug' => 'sketchbook', 'with_front' => false ),
                        'has_archive' => true,
                        'hierarchical' => false,
                        'supports' => array( 'title', 'page-attributes' )
                    )
                );
            }

    ?>