Ok. Because I'm a moderator in the group in question, I was able to go in and look at my own activity history. It turns out that I set myself to No Email in December. However, my Subscription page still shows Individual Messages, Following Only, First-Messages-Also, Auto-follow Replies, which led me (and any other group member of any other group who is so affected) to wonder why I'm getting no email.
So this is the disconnect. When I go to my subscription page, it looks like I should be receiving some emails. But I'm receiving none.
I still speculate/guess that the reason for the snafu may be the recent changes in Following Only vis-a-vis Individual vs No Email. I will downgrade my description from "bug" to "disconnect." But it is something that should be fixed.
Messages are the sole opinion of the author, especially the fishy ones.