Getting music onto my itouch

I am using iOS 8.4 on an iTouch 5th generation.

I am trying to transfer music to my iTouch. I buy an album of music through iTunes and the iTunes Store.

The album downloads to iTunes. I plug my iTouch into my Mac and select the tracks from My Music, then drag the selected items onto my iTouch.

Sometimes, everything goes the way it's supposed to. The tracks are copied onto my iTouch. Great.

But just as often, I can see the items (greyed out) on my iTouch, then nothing happens for five, ten, fifteen or more minutes. NOTHING IS TRANSFERRING.

When I look at my the Music App on my iTouch, it shows the album and tracks, but only . . . perhaps . . . two of the tracks are physically transferred to the iTouch (you can see the little iTouch icon in the corner of the track item). The others will play from the cloud, but have not been transferred.

Then sometimes, in desperation I try to drag the tracks onto the iPod again, and what appears in the Music app is two copies of each track.

What is going on? Very frustrating. Am I doing something wrong? Is the Music app flaky? Is it an iTunes problem?