Dear Petr,
The FoodBook is a fully functional individual plugin. You can’t use it only for the manager, kitchen and delivery boy without its ordering system.
Moreover, our plugin has no issue like this. You could check out the full working demo there https://themelooks.net/demo/foodbook/
As we can understand, it’s a plugin confliction issue. If you disable the FoodBook then your system works. That means your system has an issue that conflicts with FoodBook.
Please check out the issue by changing the theme that you are using at the moment. Also, deactivate 3rd party plugins to check which plugin conflicts with FoodBook.
Best Regards,
ThemeLooks Support Team