I deleted an empty folder through the website. NewsBlur sent me an email saying, “Just in case you didn’t intend to delete that folder, here’s an OPML you can upload to restore it”, which is so awesome!
But, the OPML contained all the feeds I’m subscribed to, even though I didn’t delete everything (and even though everything wasn’t actually deleted). Seems like deleting the empty folder caused something to think I was deleting everything.