To make things even clearer:
Before 2.1, the feed was showing up fine.
After 2.1, instead of the feed showing up, now it says “The feed is either empty or unavailable.”, indicating the feed is empty. But it’s not empty because the feed is showing up when I view it in my browser.
Oops, the code got parsed funky. Basically, I’m using a variation of the code on this page: https://codex.wordpress.org/Function_Reference/fetch_feed
