Homepod Audio Drop Out Playing from Apple TV

Have an issue when trying to play audio through my Homepod from Apple TV 4K. The issue occurs when I nominate my Homepod as the audio output in Apple TV settings. Once the movie starts after around 20 seconds or sooner the audio then goes silent or off and the Homepod appears to have gone to sleep. There are no volume indicators visible on the top of Homepod which means its switched to default standby mode.

Weirdly... exiting the movie back to the Apple TV interface, the sound of all the pops and clicks of the Apple TV interface are perfectly audible through Homepod???

Apple TV and Hompod are all up-to-date on their respective software updates. Obviously a streaming bug or authentication issue with Airplay?

Any suggestions or advice.

Apart from that weird issue, Homepod works great for music streaming from iTunes and the audio is amazing.

Great listening to all my music again, find I'm hearing guitar strings, notes and sounds i never really noticed before.