Blog Post Section Disappears from Customize

When I log into my account and try to customize my blog posts from the customize interface my blog posts all disappear. I can see them when I’m not in the customize screen but when I click on it I get a not found 404 error message. Even when I click on a post and try to customize it directly from the post page it disappears in the customize screen… Help!

The page I need help with: [log in to see the link]