grey dotted circle

If your library has more content than will fit on your device you might want to sync a subset of the library. There are options on the Music tab for the device that let you chose what it synced. See step 5 and the image below. Instead of Entire Library you can choose Selected playlists, artists, albums, and genres. This is in contrast to Manually manage content on your iPhone, iPad, or iPod touch using iTunes - Apple Support which is the other way to manage content, and would requires additional effort to recreate after a restore.

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You could try the following all-purpose steps for dealing with erratic device or sync behaviour (including the troublesome grey dotted circles of stalled transfers). They assume that all of the content you want on the device is in your library ready for restoring. If it isn't see Recover your iTunes library from your iPod or iOS device first. I would also recommend you copy everything out of the camera roll if you haven't already.

1. Backup device.
2. Restore as a new device.
3. Restore the backup you made earlier.

Use an encrypted backup (*) if you want to preserve passwords, Wi-Fi settings, web history and health data where appropriate. I also suggest syncing with a selection of playlists (unless you're using iCloud Music Library) rather than manually adding content as, if nothing else, the process above is easier to do if you ever have to go through it again.

(*) The downside with backup encryption is that if you forget the password when you need it again, which could be years later, you may need to invoke a workaround to turn off encryption as shown in Re: disable encrypted backups, which can only help if your device is in a state that can backup to iCloud, or runs iOS 11.

FWIW I successfully used this method some time ago when Siri became unable to call contacts or play my music.

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You're welcome. 🙂

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