I don't know how many Apple Product experts are on here but here goes:
I have a Homepod I've had for at least 2 years that's worked flawlessly until yesterday. I only use it to play Apple Music. Yesterday I changed my Apple Id which, of course effects every Apple product one owns. I have systematically gone through every Apple product I own i.e. iPhone, iPad, Apple TV, etc. insuring each is working as they should.
The Homepod is a different animal altogether. It's designed such that you remove it from the box, plug it in and it installs itself. No book, no app, etc. All well and good for the first install. In this case I'm trying to reinstall. To make matters worse, the original install put the homepod in an app called Home (for home automation). In my efforts to reinstall, I deleted the homepod from the Home app thinking a reinstall would put it back. I was wrong. So, currently:
It appears to work for all functions. If I say Hey Siri, play Frank Sinatra, Siri responds with I can't locate Frank Sinatra in Apple Music. This is the case regardless of the artist you're requesting. I'm guessing it's all due to the homepod not being in the Home app, but who knows!