This issue was addressed a couple of years ago, where radio stations stop working and the HomePod shuts off. I am close to stopping our monthly subscription to our favourite radio station because our homepod will not play it. This happens even when try to play it on my phone and cast to the HomePod.
HomePod
if it was me then I would reach out to tuneIN support, a few years back apparently some rules at BBC mean some BBC live stuff was removed from tunein and by associacion from homepots maybe it's a similar situation or maybe only a tempory issue
these forums are user helping other users like yourself, it's sort of going
to a physical apple store and asking other customers there advice
it would be staticically unlikely you would come across anyone here who had a deeper insight into the nature of the problem it be technical or intentional.
tuneIN Support : TuneIn User Support
or if you wish to reach out to apples official support channels
And or
Contact - Official Apple Support
And or
Contact - How to Contact Us - Apple
HomePod issues with TuneIn radio stations
