Hmmm… this is most bizarre! I disabled everything and it still didn’t work. Then I entered the most recent post and realized I could scroll in there either. Entered another post and all was fine. So I checked the post in the admin interface but couldn’t find anything. So I copied the text into a text editor and deleted the post, created a new one, copied and pasted the content into it and published the new post.
Now all is fine. It must have been something in the post that WordPress didn’t like.