I fixed it. The problem was the I upgraded the software and the latest version had a different way of creating the list. The function was designed to show ten or so topics, not 200. It looks at topics by looking at posts, but it wasn't looking at enough posts to add up to 200 topics (indeed, only 175 - and that's posts, so the topic list was shorter).
In any case it should be working now. Sorry to have let that problem linger for so long.