If this happens - especially if the admin bar disappears - then very likely the page was not finished by WordPress/PHP.
If you look at the source code of the page you've provided, you'll notice that it abruptly ends at a paragraph.
To debug this, you may have to edit your
wp_config.php file, and enable (or add) the following line:
WordPress/PHP will then generate extra error messages, from which you can trace the cause. Most likely you'll notice a "PHP Fatal Error", along with a line where the error is located and what the error was caused by. Note that enabling this will make the error messages visible to everyone, so use it with care on a production site.
Hopefully this will help.