Followed libraries are not returned from the API

I am experimenting with the subscribed scope used in open.audio's API. For instance, I tried calling /api/v1/artists/?scope=subscribed but an empty list was returned.

GET /api/v1/artists/?page_size=1&scope=subscribed HTTP/1.1
Accept: */*
Accept-Encoding: gzip, deflate
Authorization: Bearer [REDACTED]
Connection: keep-alive
Host: open.audio
User-Agent: HTTPie/2.2.0

HTTP/1.1 200 OK
[...]

{
    "count": 0,
    "next": null,
    "previous": null,
    "results": []
}

Following that, I also tried to call /api/v1/libraries/?scope=subscribed, with no more luck, still an empty list.

As far as I can tell, I do follow some libraries there, as the libraries' pages do show the "Unfollow" button. Something is weird though: the library page indicates I follow it, but the "User libraries" box on a track page shows the "Follow button" (see attached screens).

Am I misunderstanding the concept of subscribed content? Is it meant to be something else that the "follow" state?