Empty print page when using a custom field

Hello, I'm having a problem with print pages after migrating from Phprunner 9 to Phprunner 9.8.

I have a list page with only one field which is shown as custom field with the following code
include_once('./include/analuseis/analusi_upiresiwn_miniaia.php');

$value=$article;
The page works fine :

but when I print it I get an empty print page!

Any ideas?
Thank you in advance,

Thomas