HomePod Siri not working?

Since installing the iOS 12 betas, my HomePod stereo pair has oddly stopped responding to Siri - says it’s “Not connected to the internet” (after attempting the command for an extended period of time)

Weirdly they ARE connected to the internet, as I can control from my iPhone / Apple Music

Tried Siri on both, tried pulling power on both and restarting, no luck...

Anyone else experiencing this?

(And yes, there is no iOS 12 software for HomePod that I’m aware of so betas on other devices shouldn’t affect them, could be hugely coincidental, but just seems odd...)