iTunes 12 fails to sync audio books to iPod

Running iTunes 12.3.0.44 in a Windows 10 environment. I sync music from iTunes to the iPod (fifth generation) using drag and drop. I get the flashing blue line around the iPod icon, and then see the music being synced to the iPod. I can check the iPod, and there is the album I just dragged over to the device. I use the same method with my audio books, get the flashing blue line, and ... nothing. Any ideas? Thank you.