Cannot copy music to manually managed iPod touch
I am unable to copy music to my iPod touch in iTunes.
Setup: OS X 10.10.4, iTunes 12.2, latest gen iPod touch with iOS 8.4 and 2 GB free set to manually manage music.
In iTunes, drag copying a moderate amount of files from a playlist of files on my computer to a playlist on device results in a long "preparing to update" process. Eventually after about 10 minutes the tracks appear on iPod greyed out. These tracks are unplayable.
Deleting the greyed out tracks, waiting 10 minutes for the process to complete, then attempting to drag copy the files over again, also fails.
The files in question are pretty standard mp3 and aac tracks. The amount of files I am copying over are well under the free space on device. I have successfully copied over these same files to this same iPod in the past.
How can I copy over music to this iPod?
iPod touch, iOS 8.4, null