Download Limit

[Crucial378]

I have one main playlist that I add songs too. I organise the list by “recently added” as they are the new tracks that I listen to most. I have this list set to download as due to work I have to often listen offline. 
Now every time I add a song an old one becomes unplayable. This is ridiculous. I’ve seen similar posts going back years and yet nothing changes. Spotify have no problem increasing the cost yet they can’t sort out this simple thing. Please allow unlimited downloads as I’m losing all my old tracks.