There's a couple of different reasons why you could be seeing this happen on your Spotify account. We've explained them below, along with what some troubleshooting steps you can try.
> If you notice songs unexpectedly added on your Liked Songs:
It's possible that you've linked your Spotify account with a third party app that could be adding new songs from your favorite artists when they become available. In this case, it would be a good idea making sure to revoke access to any third party apps you don't recognize or no longer need with the steps mentioned here.
Tip: when integrating Spotify with a third-party app, always double check the permissions it allows before linking.
If you're still having troubles, we'd recommend making sure to follow the steps provided in this support site article, including reaching out to our support teams so that they can look into this for you.
> If you're on free and notice songs added on playlists you've created:
Spotify Free can help you find new music we think you'll love. That means we’ll continue to suggest tracks and artists for your playlists as you create and edit them. The more you listen, the better the suggestions will become.
Further, if you have less than 15 songs in your Liked Songs, we'll add more songs. You will see a message telling you that the extra songs were added by us, but they can be replaced by adding more songs.
For more info on stopping these suggestions, we'd recommend taking a look at this Spotify Answer.
> If you're on Premium and see artists or albums showing up below artists you follow or albums you've saved:
With the new Your Library update, we introduced Album and Artists recommendations. These will appear at the bottom of the Album and Artist tabs in Your Library.
The suggestions are based on the songs and albums you've liked but no worries! They shouldn't be added in Your Library unless you click the heart icon (for albums) or follow the recommended artists.