Have you tried removing Pandora from your music services in the Sonos app and adding it again?

I’m having the Same issue

Same issue. Tried GuitarSuperstar’s suggestion. No luck. Still denied once or twice a day, having to constantly reauthorize 

Hi folks, thanks for reaching out to the Sonos community and letting us know about your concern. Let me share this community topic for the same issue. You may follow the steps we recommended if it will work for you. If you’re still experiencing the same problem on Pandora, I suggest contacting our phone support team to look into this. Our phone support has the tools to check what's going on in your system and to remotely access your device to address the issue. Please let me know if you have any further questions or concerns, I'll be glad to assist you.