I've seen this across nine different Stacks I follow, so I presume it's everywhere.
The last few days, I've been getting a little box in most (all?) questions with a bell icon inside and "get updates on questions and answers" -- but there's no active text in the box, the bell isn't active, and the only function that appears to be available is to close the box with the X in the upper right.
Is this a preview of an upcoming feature, a bug, or a bugged/failing feature that's supposed to be live? I've looked in other parts of the UI and don't see anything that lets me specifically follow a given question or answer. What's up with the bell box?