Since all Sonos does is point their speakers to the servers provided by Frisky Radio, have you tried pinging them directly?

What do you mean by “ tried pinging them directly”

Contact ‘Frisky Radio’. I’ve never heard of them, so I don’t even know if they’re a “plugin” for Sonos directly, or you access them via TuneIn, or some other radio service.

But Sonos doesn’t “own” or “serve” 99% of the content, they just are told where to point your system to in order to get the stream. Think of Sonos like a TV set. The TV set does give you access to HBO, but the TV set doesn’t own that data, nor maintains a server of their own to provide HBO, all they do is point their “receiver” to where the data should iive. 

Alternately, you could call Sonos Support directly to discuss it. There’s always the possibility that there’s something in your network setup that may have changed without your active participation which could be blocking Sonos from accessing the servers they’re being pointed to. Especially as the way I read your post, it did work for you in the past. There’s certainly been cases in the past where updates that the user is ultimately unaware of have changed things, such as DNS servers on their router, and it requires extra effort to sort out. Sonos has the tools that can help figure that kind of thing out, but they can’t do that on a forum, you have to call in. 

Same issue here, love Frisky Music but not working since month on Sonos Radio. Via App/AirPlay it’s still working. Send them a mail but no response.