In my liked music, I have some duplicate songs. Even though the song title, artist, and album are the same (and both have the explicit tag), they are showing as two different songs in my liked songs list. I confirmed this by looking at the song and album URIs.
In the attached you'll see my example.
IV. Sweatpants by Childish Gambino
song uri: spotify:track:00GOPLxW4PGQuUYdPJh8K1
song's album uri: spotify:album:4GNIhgEGXzWGAefgN5qjdU
2nd song uri: spotify:track:2rmq49FcJ4U3wh1Z7C9UxE
2nd songs album uri: spotify:album:0zi2TaQkYxfXIBvl2yTjQJ
This is just one example of many in my library. I don't believe spotify intentionally has the same exact album/song with two different URIs. This is especially annoying when I'm listening to a song and it shows I haven't liked it. And then when I do, I now have a duplicate in my spotify library.