If is_page include/else not working all of a sudden

Question

I've had the same code on my wordpress site for more than a year, and it's stopped working. This is part of page.php:

<?php
if (is_page( 83571 )) { 
  include('adsense-schools.php');
} else { 
  include('adsense.php');
}
?>

Previously, this used to work, but today I noticed that it is not working correctly. adsense.php is included on all other pages, but adsense-schools.php does not show on page 83571. (And I have checked to make that sure that page id didn't change, the URL when editing that page ends in ...wp-admin/post.php?post=83571)

I also tried changing to page title instead of page id number, so

<?php
if (is_page( 'international-schools' )) { 
  include('adsense-schools.php');
} else { 
  include('adsense.php');
}
?>

But that didn't work either. Am I missing anything?

Answer 1

If nothing else works you can alternatively try the following:

global $post;

<?php if( $post->ID == 83571) { ?>

      include('adsense-schools.php');

<?php } ?>