This issue seems to have been resolved.
We reached out to Steam Support and Red Hook, and neither of them have any idea as to what might've caused this.
Hopefully this just doesn't happen again? If it does, we'll be sure to do our best to address it.
We're aware that Black Reliquary is not downloadable on Steam and are actively looking into it.
Based on past technical issues, we believe this may be a problem on Steam’s side.
Thank you for your patience.