Thanks for reaching out and sorry for the late response.
Quick question — is your Chromecast device shows up as Needs setup in the list of devices, or it doesn't show up in the Google Home app?
If there's any recent changes to the router, including: router password, router name, router location (it could have an effect if you move the Chromecast further away), etc., and your device shows up as needs setup, please set up the device using the Google Home app. Here's how: At the top left in the Google Home app, tap Add + > Set up device + > New device > set up new devices in your home > Follow the in-app steps.
On the other hand, if your device doesn't show up in the Google Home app, check the WiFi settings of the phone and connect directly to the Chromecast's temporary hotspot, Chromecast XXXX, or manually look for the previous name that has been used for the Chromecast device like Living Room TV or Bedroom TV, and then proceed with the normal setup.
If the device still can't be set up, proceed to do a factory reset.
Let me know how it goes.
Just wanted to see if you still need help. Please let me know if you have any other questions or concerns as I will be locking this in 24 hours if I won't hear back from you again.
Should that happen, feel free to create a new one if you have more questions or have other concerns in the future.