Unable to Airplay some content from Apple TV to HomePod

I have, within the last quarter, begun to have an issue with AirPlaying some content from the Apple TV to the HomePod. I began, first, to no longer be able to Airplay Pandora. Today, I am no longer able to AirPlay YouTube. All my video streaming services will AirPlay, as will iTunes. I have checked settings, reset both devices, checked for updates. I can go from AirPlaying sound from Hulu from the Apple TV to the HomePod, then open YouTube to listen to that while I work - and the sound will come from the TV instead of the HomePod.