Page/Post doesn’t update when I edit

I’ll publish a post or a page using one theme. Then I change the theme and publish a new post. The new post has the new theme, the first post has the old theme. It also happens when I’ve updated anything with the editor: the sidebar, header, footer, etc. It never shows up correctly with the old post. However if I go back to the old post and just hit update it is fine.

Any idea what this is?