Sticky Posts Not Sticking to Top of Category Archive

By default, sticky posts only stick to the top of the first page of the main blog posts index.

The easiest way to show sticky posts in other contexts is probably via a custom loop, e.g.:

$sticky_posts = new WP_Query( array(
    'post__in' => get_option( 'sticky_posts' )
) );

if ( $sticky_posts->have_posts() ) : while ( $sticky_posts->have_posts() ) : $sticky_posts->the_post() );
    // Loop markup here
endwhile; endif;
// IMPORTANT
wp_reset_postdata();

You would place that before your normal loop output, and wrap it in any conditionals that you might need (to account for context, pagination, etc.)