The swipe to queue and add track to library gestures are no longer working on any Artist's "Popular" songs. The gestures still work in other locations such as when viewing albums, playlists, or searched songs.
This feature is important to me because when a song comes on from an artist I haven't listened to and like, I visit artists pages and queue up their Popular songs to see if I like some of their other releases. This allows me to easily and quickly save the songs and artist if I like them or pass them up and continue with my playlist/radio if I do not. The ease of access is especially important while I'm working, exercising, or driving.
I'm guessing the loss of functionality has to do with the recent UI change to Artist's pages (Pictures are now a cover picture behind their artists names and follow button look and position change).
The iOS app was recently updated so you can now swipe to queue popular tracks on artist pages. If you don't see it yet, make sure your Spotify app is up to date.