We recently rolled out a new Your Library experience to all platforms. With it, we made some changes to the way music is saved to Your Library.
Here's a quick guide which explains how it all works.
Liked Songs (formerly Songs) :
For more info on the new Your Library experience on mobile, make sure to check out this Spotify Answer.
Didn't help? Search for more Spotify Answers, or create a new thread and ask the Community.