Certain Artists Wont' Download Offline

[user-removed]

I'm not sure if it's just me or if this is a widespread / legal issue. I have Spotify Premium, and I have a playlist selected to be Available Offline. The entire playlist has the green download arrows and were successfully downloaded. Then there is one album by one artist (Coasts by Coasts as well as their other singles) that does not have any download arrows. I know that if there is a gray download arrow that it can be downloaded but hasn't yet. Coasts just has no arrow whatsoever. Why is this, and is it an issue with iOS as well?