Hello,
Received the following reply from Help Desk:
Please find the Address block on the Checkout page layout and add second address line to checkout page.
Go to Design > Layouts, click gear button on the Address block and switch to the Content tab. I have attached the screenshot of this page.
The second address line will appear on checkout page and in the order info as well.
So when choosing to modify Profile Fields in Administration please make sure they are going to appear in your orders or you may need to modify as above.
Best
Phil