Hi @eddie. Thanks for reaching out.
Please check the Element tree section and try clicking on the Group names or the “eye” icons - some elements/groups on the design tab are hidden, so you can make them visible on the editor side manually.
Besides, some pages might be empty on the preview because the blank page itself does not contain any data and if you want to see it filled with different content - you need to start from the index page and open manually the page you wanted to preview. It is happening because a lot of groups and elements on pages contain different visibility conditions (when some condition is true when dome specific user is previewing the page, etc).
I hope it helps. Happy holidays!