Query Ignoring ‘exclude’ Parameter?

I’m running a query to dig up related posts based on tags. If CURRENT POST has tags A, B and C, show 3 more posts that have either A, B or C tags. I also only show posts that are 365 days old or newer.

$date_to_compare = date('F jS, Y', strtotime('-365 days')); 
$new_category = get_the_category();
$the_tags = get_the_tags();
$first_tag = $the_tags[0]->term_id;
$second_tag = $the_tags[1]->term_id;
$this_post2 = get_the_ID();
   $args2 = array(
    'posts_per_page' => 3,
    'post_type' => 'post',
    'ignore_sticky_posts' => 1,
    'orderby' => 'rand',
    'tag__in' => array( $first_tag, $second_tag ),
    'exclude' => $this_post2,
    'date_query' => array(
        array(
            'after'     => $date_to_compare,
            'inclusive' => true,
        ),
    ),
  );
  $the_query_2 = new WP_Query( $args2 );
  if ($the_query_2->have_posts()) :
  while ( $the_query_2->have_posts() ) : $related_post_count++;
    $the_query_2->the_post(); ?>
  // show the post content
  endwhile; endif;

This usually works really well, but there’s one case where CURRENT POST is one of only 3 posts that would match this. In that event, CURRENT POST is included in the three related posts, despite $this_post2 = get_the_ID(); and 'exclude' => $this_post2,

Thus, my conundrum.

WP_Query does not support an exclude argument. To exclude a post by ID, use post__not_in and pass it an array of IDs.

Using your code above, your arguments could look like this:

$args2 = array(
    'posts_per_page' => 3,
    'post_type' => 'post',
    'ignore_sticky_posts' => 1,
    'orderby' => 'rand',
    'tag__in' => array( $first_tag, $second_tag ),
    'post__not_in' => array( $this_post2 ),
    'date_query' => array(
        array(
            'after'     => $date_to_compare,
            'inclusive' => true,
        ),
    ),
);