The problem seems to be restricted to the CBS app. All of the others that I listed above (Hulu, HBO GO, Comedy Central, TBS, etc.) able to stream audio via AirPlay to the HomePod while the associated video feed is streams on the iPad just fine. The CBS app does not appear to support this, whether or not I open it from the Apple TV app or if I go to the control center to choose HomePod for AirPlay. No matter how I do it, the CBS video freezes when I send the sound to the HomePod. Curiously, this is NOT the case when I use the CBS app and stream the audio to a different AirPlay destination (e.g. AirPort Express that connects to a sound system). In this case, the CBS video streams properly on the IPad and the audio is available from the AirPort Express.