Pagination in a Shortcode. Get_next_posts_link not working but get_previous_posts_link works fine right next to it

I’m trying to output a custom post type archive using a shortcode. Everything works fine except for the get_next_posts_link part. The weird part is that it’s right next to a get_previous_posts_link that works perfectly.

Here’s the function

function output_tips() {
global $paged;
$paged = get_query_var('paged') ? get_query_var('paged') : 1;
$args = array( 'post_type' => 'ht_tips', 'posts_per_page' => 1, 'paged' => $paged, 'caller_get_posts' => 1, 'orderby' => 'date', 'order' => 'DESC' );
$loop = new WP_Query( $args );

$inner = '';

while ( $loop->have_posts() ): $loop->the_post(); global $post;

    $title = '<h3>'. get_the_title() .'</h3>';

    $content = get_the_content();

    $output = '<div class="testimonial">' . $title . $content . '</div>';

    $inner .= $output;

endwhile; 

$prev = '<div class="nav-previous">' . get_previous_posts_link( __( '<span class="meta-nav">&larr;</span> Previous' ) ) . '</div>';
$next = '<div class="nav-next">' . get_next_posts_link( __( 'Next <span class="meta-nav">&rarr;</span>' ) ) . '</div>';

wp_reset_postdata();

$open = '<div class="testimonials">';
$close = '</div>';
$return = $open . $inner . $prev . $next . $close;

return $return;
}

Any idea why this might be?