If some or all of the tracks in your playlist don't successfully sync, first try to sync the playlist a second time. If that doesn't resolve the issue, then it's possible that the tracks that did not sync are not eligible to be taken offline in your country.
Note: There's a known issue where playlists with more than 300 tracks may not sync in full. As a workaround, you can split the individual playlist into multiple playlists, each with fewer than 300 tracks. We're working to resolve this issue.