The TuneIn ‘ad’ is a good indication that your speaker(s) are disconnecting from TuneIn’s servers, and then reconnecting. TuneIn is perceiving each ‘connection’ as a new one, and providing your system its preroll ads.

There are several possibilities here. Things like wifi interference could be the cause. Or potentially duplicate IP addresses. In order to clear them up, the simple, albeit potentially temporary fix is to unplug all your Sonos devices from power, and reboot your router. Give the router a couple of minutes to reload everything before plugging your Sonos in to power again. This will also fix any potentially unpropagated DNS updates between your router and TuneIn, which may have changed without your knowledge. The more permanent version of this IP address fix is to assign reserved IP addresses for all your devices in your router, based on the router’s manual. It’s good housekeeping for a network in any case, and certainly won’t hurt anything, and will help your router in the long run. 
 

But if neither of those two potential fixes work, I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.