Lena Raine Otherside ancient city bug

I have explored two ancient cities in my survival world and I have now got a lot of Lena Raine music discs that are supposed to be RARE. And you are telling me that it's apparently random? This has to be a bug, surely. I literally got 4 of them yesterday and 4 of them today. Fix this. There's no way that it isn't a bug and it's random.