Hi there scratchypants,
Since restarting doesn't resolve this issue, you may need to reset your Apple TV 4K and test to see if this issue continues after it has been put back to factory settings. If the issue is with tvOS, that can help resolve this. If needed, the steps below show how:
"Reset your Apple TV 4K or Apple TV HD
- On your Apple TV, go to Settings > System > Reset.
- Choose a reset option:
- Reset: This option is the fastest way to return your Apple TV to factory settings. This option doesn't require an Internet connection.
- Reset and Update: This option returns your Apple TV to its factory settings and installs software updates. This option requires an Internet connection.
3. Keep your Apple TV plugged into power until the Reset process finishes. Then you can set up your Apple TV again."
Those steps are from this article: Reset or restore your Apple TV to its factory settings - Apple Support Let us know if that helps resolve this or if you've already tried that.
Take care.