Homepod keeps disconnecting from Apple TV 4k and starts playing music from my itunes

I have the ATV 4k - and recently added a homepod - the sound is awesome when the homepod works with ATV. I've set up the homepod on airplay in ATV, and in the Home Hub App and it works for a while. However, in less than an hour the homepod will switch over to playing songs from my itunes account and disconnect from the TV. When it does this, in the home app the homepod shows "unresponsive". I have an ipad, iphone, the ATV, and now the homepod -who should be the "boss" of the hub? ATV? Homepod, the Ipad? What can I do to keep the Homepod playing through the ATV, not switching over to my itunes?