Viewing IMovies in photo app on. Apple TV issues

Post the end of the Theater feature on Apple TV I have been moving my home video movies made on iMovie into the photos app. Most play fine but some result in an error message. It says this format is not compatible with Apple TV . But they play fine on iPad, Mac and laptop. All seem to be in .mov format . I am moving the photos over from Apple TV file . Where am I going wrong?