The whole system is seriously broken. I have a very long playlist, the first song of which is No Woman, No Cry by Bob Marley. It plays fine, but I've been trying to download it for days. No joy. Suddenly, and just now, I was able to download it.
Another song on the playlist is Don't Think Twice by Susan Tedeschi. It won't play from the playlist, but if I search for Susan Tedeschi it will display her songs and I will be able to play it from there.
So, not available in my country (Thailand) when played from a playlist but very available when played from a search. Does that make any sense?