I have a Drupal test site with a problem on the front (home) page.
There's a sticky page node in the content of the page titled "Our Mission" - see here:
Between that page and the primary links on the header is a mystery empty div which has somehow been created along with the "Our Mission" page:
That div inserts an empty block which you can see on the page. Problem is, I have no idea how to edit the actual HTML to get rid of it.