I get this all the time too. Wish I knew a solution, but it drives me crazy that I can only get the full remote to work like 10% of the time. Makes me miss my Roku app.
Android TV Remote Service on your Chromecast is out of date.
Update the the Google home app on your iOS device.
What's your TV model? (that the CCwGTV is connected to)
I’ve had this issue a couple of times and solved by clearing cache/data on the remote app on the TV
Open the play store and update the apps. There's one inside that's the remote service and it needs to be the latest version to communicate with the remote app on phones.
Full remote unavailable. Make sure your device has latest software.
This is the message I get every time I try to connect and remote control it from iOS.