I just responded to a comment on my “model systems” post from earlier today–thereby causing the post to vanish! I have no idea what happened, I’m working on it.
UPDATE: It fixed itself. Then recurred again when I tried the same thing again. So I stopped doing that thing (which is something I’ve done many times before), and it fixed itself again. Still not sure what the problem was, but hopefully it won’t recur as long as I avoid responding to comments using what has suddenly become the Reply Form of Death.