Thanks for posting here in the Google Nest Community.
I know how it feels when something isn’t working as it should, so let’s get this resolved. A few things: which Chromecast device? What's the LED light status (solid or flashing white)? What's the distance between the router and the Chromecast device? What messages does the TV display? Does it display Set me up?
You can refresh the mobile phone, Chromecast and your WiFi router to refresh all devices and the WiFi signal. Once they are booted up observe if the issue remains.
Keep me posted.