Wanting to save songs from the Apple "Disco deep cuts" playlist, whose songs can come and go, I created a playlist called "Disco deep cuts (saved)". I was able to save about a dozen songs to it. Tonight, while playing more songs from the Apple playlist, I was unable to add some of these songs to my "…(saved)" playlist; every time, the popup would state "0 songs added to "Disco deep cuts (saved)"".
What's the problem? More importantly, what's the solution?