After server move: 'logoff page isn't redirecting properly'

[ttfan]

v1.5.5d
PHP 7.0
Theme: responsive sheffield blue
Plugins: Products with attributes 1.5.4, Google Captcha
Site: In signature
Site runs full SSL

Moved site (full cpanel account move) from one provider to another provider due to some security issues with Paypal.
The old server ran PHP 5.4.

New site works perfectly, except that after I log in, and then log out, I get a " logoff page isn't redirecting properly" error from the browser. It does actually log me out, but this error is annoying and looks unprofessional. I raised this issue in someone else's thread here https://www.zen-cart.com/showthread....properly/page3 , got a few suggestions, but unfortunately it's not fixed, so I'm hoping a few more people can offer some suggestions in a new thread, where I can present all the relevant information.

Note:

• 'fix cache key' did not work (not required for v1.5.5 anyway).
• .htaccess (root) disabled does not fix it.
• the logout page works fine when you're not logged in
• configure files have been checked - they have not changed from the other server.

Here is the (unmodified) code for the logout page:

<?php
/**
 * logoff header_php.php 
 *
 * @package page
 * @copyright Copyright 2003-2006 Zen Cart Development Team
 * @copyright Portions Copyright 2003 osCommerce
 * @license http://www.zen-cart.com/license/2_0.txt GNU Public License V2.0
 * @version $Id: header_php.php 5403 2006-12-27 00:38:58Z drbyte $
 */

// This should be first line of the script:
$zco_notifier->notify('NOTIFY_HEADER_START_LOGOFF');

require(DIR_WS_MODULES . zen_get_module_directory('require_languages.php'));
$breadcrumb->add(NAVBAR_TITLE);

/**
 * Check what language should be used on the logoff screen
 */
  $logoff_lang = ($_SESSION['languages_code'] != DEFAULT_LANGUAGE) ? 'language=' . $_SESSION['languages_code'] : '';

/**
  * Check if there is still a customer_id
  * If so, kill the session, and redirect back to the logoff page
  * This will cause the header logic to see that the customer_id is gone, and thus not display another logoff link
  */
if (!empty($_SESSION['customer_id']) || !empty($_SESSION['customer_guest_id'])) {
  zen_session_destroy();
  zen_redirect(zen_href_link(FILENAME_LOGOFF, $logoff_lang));
}

// This should be last line of the script:
$zco_notifier->notify('NOTIFY_HEADER_END_LOGOFF');
?>