I had added a plugin based on this documentation: File URLs | Kirby CMS to use “friendly” file urls rather than uuid-based urls. For some reason that works fine on my local environment, but not in production. (Even though the image and pdf file are where they are linked to in the html, so still mysterious to me.) Anyway removing that plugin solved the issue with “not found” images and pdfs. I used the solution here: Page links not working in text blocks to output friendlier file urls.