Google has issued a fix for a “Untrusted device” error affecting older Chromecast models, including the second-generation Chromecast and Chromecast Audio. The patch will be rolled out over the next few days, with users advised to keep their devices connected to Wi-Fi to apply the update. Newer Chromecast devices were not affected by the glitch.
Source: https://www.pcworld.com/article/2636937/google-issues-a-fix-for-chromecast-untrusted-bug.html