I have this for an entire album and noticed they are Apple MPEG-4 and guessing this might have something to do with it.
If I'm not wrong it looks a lot like the "downloading" icon, you have this until it is fully downloaded. But you can start play it even if it's not finished but it started.
That can happen too with video.
See this thread. They had the same issue -
Funilly his icon isn't in the icons list listed in the other thread, or at least I didn't saw it. But that list doesn't show icons for stuff downloading or to download. His icon seems related to that. I think I saw it for video, not sure for music.
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