Chromecast (2nd gen) and Audio cannot Cast in 'Untrusted' outage [Update]
9to5google.com
Over the past few hours, owners of the Chromecast (2nd gen) and Chromecast Audio haven’t been able to Cast any audio or video content.

I was wondering why my Chromecast was suddenly untrusted. An update seems to have knocked off older Chromecast devices globally. People are factory-resetting them before they know what to do, making the potential fixes even harder.