It can happen that texts such as “Steuerfreie Ausfuhrlieferung gem. §4 Nr. 1b UStG.” are not displayed on the invoice. If you're using Shopware version 5.1.2 or higher, this is most likely because you're using a custom document template that isn't configured to be overwritten by plugins. To change this, please add the following line to the theme.php file of your template, or adjust the corresponding line accordingly:
protected $injectBeforePlugins = true;