Syncing music

Are you syncing over USB or via Sync Library AKA iCloud Music Library?

See Identify cloud status icons in your music library on your Mac or PC - Apple Support. Tracks that are ineligible, waiting, error, etc. won't sync over the air. File > Library > Update iCloud Library may help with tracks that are waiting.

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Restore them from backup? Were they stored locally on at least one computer, or were you relying on the cloud?

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