Zend-Mailer does not Support BCC on SMTP transport. It drops the Bcc header before sending the mail.
A solution could be to clone the mail and replace the receiver
Open Plugin-Manager and press the Button "Synchronize licenses". When the button does not exist in your used Version:
Login in your Shopware Account in Plugin Manager
Clear all cookies of the Page
Login in your Backend
Licenses should be now synchronized in Background
Can be only fixed with an Update to Shopware 5.4.0
The Security Plugin "SwagSecurityHotFix201701" drops in newer version all fields. It can be uninstalled and removed from System
This issue happens on MariaDB Installations. You should switch to MySQL or update to the newest Shopware version.
Maybe you have a empty character or line in your config.php at <?php tag