Thanks for the feedback!
In hindsight, I probably shouldn’t have put the main part of the game into only two passages, using the visit count to display different parts of the present storyline (given how that seems to have broken the progress feature). Also, in hindsight, I probably should’ve implemented the continue button differently (as Harlowe’s restart button turns out to have a bug where it doesn’t actually restart the game from the beginning if the (save-game:) and (load-game:) macros were used).