I put in more placeholder content in the master page, and that displays, so there doesn't seem to be anything wrong with the master page not displaying anything at all. However, no pages that connect to this master page will show the content that originally went missing.
The most unusual thing is that when I go into the editor, everything appears like nothing is wrong! Content placeholder is there, content is there, everything's fine. While absolutely nothing in the content placeholder loads in the browser.
What might be causing this problem?