Songs being replaced

So recentlv I've noticed that with stats.fm when I listen to too little to late by laufev it replaces the song with clockwork by laufey, and I dont completely understand why that is happening because I have a Playlist that repeats 2 songs tough luck, and toc little to late. And when I went into my my history I saw the pattern of my music was off because I should be tough luck then too little to late. But its turning into tough luck, clockwork which I find odd