My feed was broken. It’s been broken for over a week.
I finally took a few minutes to deactivate and reactivate all of my plugins, and sho’nuff, Related entries for feeds broke my feed. So, if your feed is broken and you’re getting an error like this:
XML document structures must start and end within the same entity
And you’re seeing CDATA is open and won’t close, then you need to deactivate your WordPress plugins and reactivate them one by one, validating your feed until you figure out what broke it.
Life Lesson #5,247 brought to you by the letters R and S.