I have tried troubleshooting and googling this on my own with no luck. I have AppleTV 5K and another AppleTV (4th gen), both running tvOS 11.2. When I view my libraries under "Discover" and "Recently Added" it shows the videos just fine, but when I go to view "All" for a library it comes up empty. I've tried deleting my libraries and re-creating them and that doesn't work. This occurs for both Movie, TV and Other Media libraries.
I've know it's developed separately, but the "All" feature under Plex for Roku works fine. So I don't suspect it's a server or library issues, unless I am missing something.