Well, thank you for answering.
Now that I joined a Multiplayer game and tried it again, the map did work. Turns out it seems to be a Singleplayer-only issue. I don't know if some of the small updates in recent days changed anything about it, but once I checked I might be able to post the report in the right place.
Anyway, same thing with "remote exploring". In Multiplayer I do have things appear when I order another ship on the overview map... in Singleplayer I don't. Bummer.