There have been reports of syncing issues with iTunes, affecting music purchases regardless of the source. Our research has led to a solution that appears to be effective.
It may be beneficial to save this information for future reference.
Ensure that both your mobile device and iTunes are updated to their latest software versions.
Attempt to sync your mobile device multiple times, as this often resolves errors preventing songs from syncing.
If the issue persists, save a copy of the problematic song(s) on your Desktop by copying and pasting the file from your iTunes library. Right-click the song in iTunes, select copy, then right-click on your Desktop and select paste. If the music was purchased from us, a copy might already exist in your Downloads folder. It is important to have the song saved OUTSIDE of iTunes. Proceed with syncing your mobile device without the songs in iTunes.
Re-add the song(s) to your iTunes library using this method: In iTunes, click File on the top menu bar. From the drop-down menu, select ADD FILE TO LIBRARY. Navigate to the location where you saved the songs, whether on your Desktop or in your Downloads folder. Select the file name and choose Select File at the bottom of the box. Repeat this process for each song or highlight multiple songs to add them simultaneously. The songs will appear in your Recently Added playlist, and you can move them to any desired playlist.
After re-adding all songs, perform another Sync. Our tests indicate that this method resolves the issue. You may need to sync multiple times if necessary.