I have the problem where one playlist won't fully download, like it gets stuck on one song or something. Tried switching both wi-fi on/off - they're always off though because nothing will download otherwise. (Seems to be a Google app problem because Photos also has issues backing up if the wi-fi option is selected.) Anyway, I've deleted and re-downloaded the playlist multiple times, but it always hangs and keeps trying to download. It's a big issue because it'll sit there trying to download forever and kill the battery as a result. Wish there was an easy way to find the offending song and remove it from the playlist.
Other weird thing is if I delete it and start over, it will say Download Complete - even though the orange circle and checkmark aren't there, and it still has a partially filled circle with the download icon. And if I go to Manage Downloads, it'll start downloading again and stay at 0% progress forever. Frustrating.