Is this about Home Sharing?
Are all devices connected to the same home network? Verify your router settings that it doesn’t create multiple networks (e.g. multiple SSID Wi-Fi network names). Recommended settings for Wi-Fi routers and access points - Apple Support
Try restarting your router.
Verify that the matching Apple ID account is used for the Home Sharing settings on all devices.
Verify that all Home Sharing libraries on the networked computers have unique names.
Or is this about iTunes Store libraries (purchased content)?
If so, then try signing out, and immediately sign in again.
Verify that the matching Apple ID account is active, in case of multiple users on that Apple TV box. Other accounts can’t access your library directly.