When my webhost upgraded something, at some point during the past year—probably the database underlying this WordPress installation—the upgrade rotated Unicode code points a notch or two, such that — displays as — instead of — = em-dash.
Though I won’t clean up the old note-taking/event posts, a few pages I care about are queued for tidying.
This is the type of thing that inclines one towards exploring a static type generator, when one doesn’t really need as much as WordPress has become.