Probably down to the BBC changing its streaming formats. There are numerous Internet comments on this, so I needn't say more here.
Suffice it to say that users of an affected platform need to pester their manufacturer for the earliest possible support for HLS (
HTTP
Live
Streaming) which appears to be the BBC's medium term solution for high quality (320kbs AAC) streaming in the UK.
The upside of this mess is that all the BBC's radio services (including locals) are now available at 320kbs AAC. It's worth stating that HLS is not an audio format in itself, rather a wrapper in which the AAC or MP3 stream is delivered. The necessary URLs have been released on the Internet and are of the form
http://a.files.bbci.co.uk/media/live/manifesto/audio/simulcast/hls/uk/sbr_high/ak/bbc_radio_three.m3u8
It's probably a question of getting Sonos and its partners to offer the necessary support. Good luck.