I enjoy streaming my iTunes music library to my Apple TVs (and connected speaker systems.) On my 4th generation Apple TV, the home sharing feature frequently can’t find the music library on my Mac. The Apple TV insists that iTunes Home Sharing needs to be turned on. It’s on Apple, it’s on! Apple has many recommended solutions to fix home sharing issues, but I found a simple solution that worked for me. I just restart my Apple TV, and voila, I’m back in business! On the 4th gen Apple TV, go to Settings->System->Restart.
Update 6/27/17: The Home Sharing bug appears to be fixed on the tvOS 11 public beta. (Don’t install the beta firmware on your primary Apple TV. You may face app compatibility issues. For example, the DirecTV Now app crashes upon opening.)