This is an issue specifically with paired HomePods.
Each tvOS update brings changes in how Apple privately works with HomePods. This happens every year. They make changes, and we have to chase the changes to get them working as well as we can.
The reason other apps work just fine is because they're using the system player, so it all just works for free.
Channels does not use the system player. We have to work with making the HomePods happy ourselves, without Apple's help. It's all a big secret, and they, across 4 years, have never been willing to help, despite us reporting multiple bugs that they have even confirmed. So we just wait for them to maybe fix them.
So, HomePod support continues to be experimental, if not officially unsupported, for Channels.
We'll do another round at trying to make it better now that a new revision has rolled out, but if you're an Apple TV owner that pairs their HomePods with it instead of using regular speakers, you can expect to have troubles like this.
I can promise you, it's not from a lack of trying.