Soundiiz is using the Amazon Music API provided by Amazon to read and write data in an Amazon Music user account.
While we are adding/deleting songs to an Amazon Music playlist, it's possible that these changes are not immediately applied to the playlist. That means, on Soundiiz side for example, it's possible that you do not see new additions to your Amazon Music playlist.
We recommend you check directly on the Amazon Music website to see updates made to your playlists. Be aware that in the Amazon Music mobile app or desktop, you must refresh/clear your cache to have the latest updates on your collection.
Also, be aware that Amazon Music has a limit of 2500 tracks per playlist.
About "Tracks" collection that Soundiiz can retrieve, be aware that we can only retrieve your Amazon Music "Liked Songs" tracks with the Amazon Music developer's access. We are not able to retrieve your Amazon Music "Library songs".