Thanks for reaching out. You may try to reboot or factory reset your TV. If the issue persists, I would suggest reaching out to Vizio support for additional help since the changes in the features and settings of the TV that has a built-in Chromecast are decided by the manufacturers. You may contact them here.
We understand that this is isolated with the ambient mode feature on your Vizio TV. Please note that we have very limited support on TV's with built-in Chromecast. If you're thinking of buying a separate Chromecast device, you may visit our Google Store. Let us know if you have other questions and concerns — we're here to help!