Wasn’t even looking for this problem (my picture edges are cut off from my TV) but I had the same exact issue just now. Like, how did I even setup my chromecast without the home app? Of course I used the home app. Where is my chromecast? Why is it magically not on home app anymore?
Thanks for reaching out and I'm sorry to hear that you're having an issue with your Chromecast. Let's sort this out.
A few questions — what's the LED status on your Chromecast (solid or flashing white)? What's the distance between the router and the Chromecast device? What is the make and model of the mobile device you're using to set up your device? Please manually connect to the Chromecast SSID. Here's how: go to the phone settings > Open Wi-Fi and connect to the Chromecast SSID (Example: Chromecast1234, Living Room TV, Bedroom TV, etc.) > Go to the Google Home app and try to set it up again.
I haven't heard from you so I’ll be locking this thread after 24 hours. If you need help in the future, please feel free to start a new thread and we'll be happy to help.