The image shows that there are not controls to one of the content place holders. As far as I see it there are some controls added to the master page like the navigation menu and the logic control.
Could you try to use a clean master page - the default one without any css and js on it, then drop GenericContent control on a page and enter some text. Afterwords, save the page and then edit it. There could be something in the master page or you have some code that dynamically adds,removes or hides controls.
Are you able to reproduce the issue on demo.sitefinity.com
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