Thanks for reaching out. Let's sort this out.
A few questions: What type of Chromecast device do you have? Are you mirroring your phone's screen to your TV? Are you doing it using the Google Home app? What is the make and model of the phone you are using? Please reboot your Chromecast and reinstall the Google Home app. Resetting your Chromecast might also help.
I think it's the Chromecast Ultra, and yes, I'm mirroring the Samsung smartphone to my Vizio Smart TV. It's always worked before, just not recently (or rather intermittently). The smartphone and Google Home app are in sync, in that that graphics are lined up, and the 50Hz TV mode changes as well.
I've reset the Chromecast, yet I haven't uninstalled/reinstalled the Google Home app.
The particular smartphone is Samsung Note Ultra S20.
Sorry for the late response. If you haven't tried reinstalling the Google Home app, please try to do it to see if it'll do the trick and check for software updates on your phone. It's best to have updated applications and OS for a seamless experience. Using a different mobile phone might also help.