Any reason you edited page.php? Try replacing it with the original code: https://themes.svn.wordpress.org/generatepress/1.2.4/page.php
If that doesn’t work, you probably have an unclosed HTML element within your content.
This means you may have opened a
<div> without closing it (
That can cause the layout to go out of whack because it disrupts the flow of the HTML.
Let me know 🙂