I finally solved my issue by deleting public_html/themes/default-bootstrap/mails folder and clearing booth browser and PS cache.
My error_log was something like this:
.....
PHP Fatal error: Uncaught --> Smarty Compiler: Syntax error in template "/home/wwwmbind/public_html/site_name/themes/default-bootstrap/mails/ro/order_conf_product_list.txt" on line 2 "{$product[\'reference\']}" - Unexpected "\" <-- thrown in /home/wwwmbind/public_html/site_name/tools/smarty/sysplugins/smarty_internal_templatecompilerbase.php on line 2
Thank you.