Q: No Network Available Photos App

You might check the settings under Accounts->iCloud, and confirm that your iCloud Apple ID and password are correct.

Check the docs: http://help.apple.com/appletv/#/atvb399f3391

Force quitting the Photos app might have been enough to do it. Some apps seem to become corrupted after running for a while, and they don't exit until you force them, just like phone apps. And yes, this represents a bug in the app.

I had this problem too.

Solved with the next steps.

1. Goto Settings

2. Select Accounts

3. Select ICloud

4. Select Sign Out.

Reboot the Apple TV  ( settings,system,restart)

After rebooting

sign in your iCloud ( step 1 t/m 3)

turn on iCloud Photo Library

turn on icloud photo sharing