Shortcode that doesn't work with tax_query

// Current problem: doesn't seem to use the tax_query. No idea why. I've confirmed that $cat is the right value and is getting passed to the query.
// Expected output: 3 pages with the term I've been using for testing
// Real output: All published pages, ordered by menu order...
<?php
$pl_args = array(
    'post_type' => 'page',
    'tax_query' => array(
        array(
            'taxonomy' => 'seg_proj_cats',
            'field' => 'slug',
            'terms' => $cat
        )
    ),
    'orderby' => 'menu_order',
    'posts_per_page' => -1
);
$pl_pages = new WP_Query( $pl_args );

if ( $pl_pages->have_posts() ) : while ( $pl_pages->have_posts() ) : $pl_pages->the_post(); ?>

    <a class="seg-proj" href="<?php the_permalink(); ?>"><?php the_title() . the_post_thumbnail( $post->ID, 'react-thumb' ); ?></a>

<?php endwhile; endif; wp_reset_postdata(); ?>