subscribe.php not working (no content)

The output of the subscribe.php template seems to be broken. The page is overtly working (no 404, title is OK), but there’s no contents at all. Obviously the link supplied is just the raw permalink with no query parameters – but it’s blank even when you get there via a link with correct query parameters.

I’ve tried deactivating and reactivating the plugin to no avail. Any ideas?

The page I need help with: [log in to see the link]