My 3rd generation Apple TV has a small but annoying problem where it defaults to the National Geographic screen saver, regardless of what is set on the Screen Saver page.
I've chosen > Photos > Explore:
The next panel shows that I've chosen Flickr (but the situation is identical if I instead choose iCloud photos).
After the Apple TV has been idle for 2 minutes the screen saver starts. Sometimes it shows 1 image from Flickr then immediately goes into a loop showing the National Geographic photos. Sometimes it shows Flickr photos for ~5 minutes before showing National Geographic.
The OS is set to automatic updates and there are no other issues. It's not exactly a show-stopper bug, just a bit annoying.
(This is the same problem as Screen saver settings keep defaulting back to National Geographic Photos but applies to Apple TV, not Mac.)