Thanks for posting here in the Google Nest Community.
I know how it feels when something isn’t working as it should, let’s get this resolved. A few things: are you casting to your Nest display or Chromecast? If so, which Nest speaker or Chromecast? What is the exact message that you are getting when you try to cast?
You can reboot your phone and your WiFi router to refresh.
Let me know how it goes.