No PHP/Smarty errors are logged after white screen

[Hasher]

I am unable to localise the error, missing class/file or other mistake I could made, because nothing is added into my /var/log/php_errors.log when the white screen occurs.

 

The error itself is irrelevant here and probably trivial, more important for me is why the white screen doesn't return any errors?

 

 

In my /etc/php5/apache2/php.ini I have:

 

display_errors = On, log_errors = On error_log = /var/log/php_errors.log

 

phpinfo() returns the same values

 

 

 

/var/log/php_errors.log does log some errors in other pages

 

 

In my [Prestashop_dir]/config/defines.inc.php I have

define('_PS_MODE_DEV_', true);

 

and in smartyadmin.config.inc.php I also added

$smarty->debugging = true;

 

URL of the page that is causing the white screen:

 

[Prestashop_backend_url]/index.php?controller=AdminPdf&token=d10cf8b3819b0922610f36caf0e37c24&submitAction=generateDeliverySlipsPDF&id_order=1