An Austrian developer managed to get his entire data archive from Spotify. The man realized that company was tracking his every movement. It is normal for apps to collect some data to improve user experience, provide better support and develop new products. However, Spotify tracks other information, that users would not assume it serves the mentioned purpose. For example, what brand of headphones you are using, at what point within songs did you change the volume and all user interface actions. As the music app seems to be collecting every possible data from their users, there is a high chance that they may be infringing the data minimization principle in GDPR.
LEARNING TIP: Inform clients about all the personal data you are collecting, and the processes done to it. The information should be in the Privacy Notice.