[Resolved] Custom Archive Page Template Issues

Hi,
I’ve setup a custom page template so I can list posts from 2 categories on a particular page. However, although all the correct posts are displayed, the featured image thumbnails are not displaying and neither is the pagination at the bottom of the page. I used the category.php as a starting point and just edited it and renamed it page-archive.php, see my code below:

<?php
/**
 * Template Name: All Routes
 *
 * @package GeneratePress
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit; // Exit if accessed directly.
}

get_header(); ?>

	<div id="primary" <?php generate_content_class(); ?>>
		<main id="main" <?php generate_main_class(); ?>>

			<?php
			/**
			 * generate_before_main_content hook.
			 *
			 * @since 0.1
			 */
			do_action( 'generate_before_main_content' );

			$args = array(
					'cat' => '1,4',
					'posts_per_page' => 8

			);

			$routes_posts = new WP_Query( $args );

			if ( $routes_posts->have_posts() ) :

				/**
				 * generate_archive_title hook.
				 *
				 * @since 0.1
				 *
				 * @hooked generate_archive_title - 10
				 */
				do_action( 'generate_archive_title' );

				while ( $routes_posts->have_posts() ) : $routes_posts->the_post();

					/*
					 * Include the Post-Format-specific template for the content.
					 * If you want to override this in a child theme, then include a file
					 * called content-___.php (where ___ is the Post Format name) and that will be used instead.
					 */
					get_template_part( 'content', get_post_format() );

				endwhile;

				generate_content_nav( 'nav-below' );

			else :

				get_template_part( 'no-results', 'archive' );

			endif;

			/**
			 * generate_after_main_content hook.
			 *
			 * @since 0.1
			 */
			do_action( 'generate_after_main_content' );
			?>
		</main><!-- #main -->
	</div><!-- #primary -->

	<?php
	/**
	 * generate_after_primary_content_area hook.
	 *
	 * @since 2.0
	 */
	do_action( 'generate_after_primary_content_area' );

	generate_construct_sidebars();

get_footer();

Any help appreciated.