Purchased music missing
I purchased the movie soundtrack for "Dan in Real Life" - played and enjoyed it a lot over the past five years or so, and now in the library I see that half the songs are missing.
MacBook Air 13", macOS 10.14
If the version of the album that you bought is still in the store (and if you haven't moved countries since buying it) : Redownload apps, music, movies, TV shows, and books from the App Store, iTunes Store, and Apple Books - Apple Support
If it doesn't show there check to see if you've hidden it : Hide and unhide music, movies, TV shows, audiobooks, and books - Apple Support
Or copy it back from your backup of your downloads/computer