You likely have an extension that typically loads at the top of the page, like a toolbar or overlay. I've seen similar from things like VWO, SEO toolbars and ev

You likely have an extension that typically loads at the top of the page, like a toolbar or overlay. I've seen similar from things like VWO, SEO toolbars and even Wordpress. When they're not needed they sometimes hide themselves REALLY badly, creating a gap at the top of the page on certain sites.