Part of the problem seems to be the page is VERY VERY VERY big and I don't know why.

Hi Russell thanks for posting in the Lucidspark Community I am happy to help! For security reasons I have deleted the URL from your original post.

This issue may occur when you have shapes placed on opposite end of the board. It looks like there is a stray shape on the other end of your board. Since the export tries to display all shapes on the board the shapes are at the very top left and bottom right corners of the export which is what causes your export to appear blank. 

To locate and delete the stray shape click and drag your mouse from the very top left to the very bottom right corners of the board. This will mark all shapes in a blue box at the bottom right of which you can find the stray shape. Once the shape is deleted your Mini Map and export should display the rest of your shapes properly.

The below screenshot that includes the open Mini Map displays where in the canvas this shape is located. 

For more information on how to open the Mini Map please take a look at the Getting Started with Lucidspark article in our Help Center.