iTunes Not Transferring Songs

This started a few days ago. Spoke to senior level at Apple Support, they had no solution. I also exchanged iPad. Still having problems. When I purchase any song on iPad from iTunes it downloads right away and also shows up on computer but the song does not transfer to iPhone or iPod Touch. I am logged on same Apple ID across devices, automatic downloads (music) is clicked. Furthermore, If I purchase on computer it shows right away but won't reflect on any device except iPad.. there it's grayed out and get the "item not available" pop up when trying to play. Is this a bug or possible issue with Apple ID? Hoping someone here can assist.