Pandora responded and are in the works with a fix. Here’s a work-around from Pandora Support, “In the meantime, I suggest streaming to Sonos with the Pandora app. To do that, make sure you're connected to the same Wi-Fi network as your Sonos device, and open the Pandora app.
You'll see a casting option (a rectangle with diagonal lines) on the Now Playing screen. Tap it to initiate a connection with your Sonos device. Once you've connected successfully, the casting icon will appear filled in, and a new navigation screen (or "device shelf") will appear. This shelf will allow you to edit your Sonos groups, select which devices to play through, or control the volume of your devices.
Just click on Show Group to make edits to the currently playing devices, or Edit to make changes to other groups.
