Many Sonic Soundtracks Disappear from Spotify

Only a month after a steady stream of Sonic soundtracks surfaced on streaming service Spotify, many subscribers are surprised and saddened at the sight of those songs saying sayonara without some prior notice. (Say that three times fast!)
Fans report music from titles like Sonic Rush, Sonic Generations, Sonic Lost World, and more have mysteriously vanished. In some cases, they have been replaced with a single track from the album instead of the entire work.
Other Sega titles, such as Jet Set Radio, remain on Spotify.
We asked Aaron Webber of Sega what was going on, and he told us he will look into the matter:

@tssznews I'll look into it for you! More news as soon as I have it.

— Aaron Webber (@RubyEclipse) December 18, 2015

We will update you when we have an answer.