Page 2 of category page in only some categories not working

Please see https://temp.donelsonhills.com/category/association-meetings/

If I advance to page 2 then

get_header(); ?>
JOINUS
Illustration: Phil Ponder
Site design and development: Matthew Madden

is echoed to the screen. On the Beautification Projects category page, clicking on the next page returns the next 6 posts as expected. Only a couple of the second category pages are failing. The rest seem to be working fine.

Below is the code for the category.php file…

<?php get_header(); ?>
<div class="welcome"><?php wp_title(""); ?></div>
<div class="content">
	<?php
	$thecatid = get_query_var('cat');
	$args = array(
		'paged' => get_query_var('paged'),
		'cat' => $thecatid,
		'posts_per_page' => 6
		);
	$the_query = new WP_Query( $args ); ?>
	<?php wp_pagenavi(array( 'query' => $the_query)); ?>
	<?php while ( $the_query->have_posts()) : $the_query->the_post(); ?>

	<div class="homePosts">
		<h2 class="postTitle h2"><?php echo the_title(); ?></h2>
		<?php
		if ( get_the_post_thumbnail($post_id) != '' ) {
			echo '<a href="'; the_permalink(); echo '" class="thumbnail-wrapper">';
				the_post_thumbnail('medium');
			echo '</a>';
		} else {
			echo '<a href="'; the_permalink(); echo '" class="thumbnail-wrapper">';
			echo '<img src="';
			echo catch_that_image();
			echo '" alt="" />';
			echo '</a>';
		}
		?>
		<?php the_excerpt(); ?>
	</div>
	<?php endwhile; wp_reset_postdata(); wp_reset_query(); ?>
</div>
<?php include('sidebar.php'); ?>
<?php get_footer(); ?>

Any help is much appreciated.

https://www.ads-software.com/plugins/wp-pagenavi/