I’m now wondering which radio station you are referring to here and how you launch the station (i.e. from a saved favourite, or direct from the installed tune-in service in the music services tab in the Sonos app etc. )?

Usually, that ‘pre-roll’ advertising is inserted by TuneIn when it perceives a new connection, which suggests there’s possibly some new wifi interference affecting the ability of your Sonos speakers in reaching the appropriate server to get the stream. I’d recommend reading the linked FAQ and seeing what potential changes you might apply. Note that all interference doesn’t necessarily come from within your home, I had an instance where a neighbor set up a new router that stomped all over the SonosNet frequency I was using at the time.