show white page after create post or…

Hello
Please help me for this site:
https://amirindustrialgoods.ir/

when create post or change option show white page but Success.
if delete functions.php for theme so good working and no show white page

Content file functions:

<?php add_theme_support( 'post-thumbnails' ); ?>
<?php date_default_timezone_set('Asia/Tehran'); ?>
<?php
function wp_pagenavi() {
  global $wp_query, $wp_rewrite;
  $pages = '';
  $max = $wp_query->max_num_pages;
  if (!$current = get_query_var('paged')) $current = 1;
  $args['base'] = str_replace(999999999, '%#%', get_pagenum_link(999999999));
  $args['total'] = $max;
  $args['current'] = $current;

  $total = 1;
  $args['mid_size'] = 3;
  $args['end_size'] = 1;
  $args['prev_text'] = '?';
  $args['next_text'] = '?';

  if ($max > 1) echo '
<div class="wp-pagenavi">';
 if ($total == 1 && $max > 1) $pages = '<span class="pages">???? ' . $current . ' ?? ' . $max . '</span>';
 echo $pages . paginate_links($args);
 if ($max > 1) echo '</div>

<pre>';} ?>

Please help me, to solve the problem
Thanks

[ Moved to How-to and Troubleshooting ]