Last week, there was a global outage that affected the Chromecast (2nd Gen) and Chromecast Audio, causing frustrations for many users. Google promptly acknowledged the issue and began working on fixes. An initial fix was quickly rolled out before the weekend, which helped most users, unless they had performed a factory reset during the outage. For those who did reset their devices, a separate fix was required.
Today, Google provided an update for Chromecast (2nd Gen) and Chromecast Audio owners who had factory reset their devices. They announced that a Google Home app update (version 3.30.1.6 for Android and 3.30.106 for iOS) will resolve the issue. The app rollout has started and may take a few days to reach all users.
If you reset your Chromecasts last week when they stopped working, this update will fix the problem. However, Google mentioned that it may take a few days for everyone to receive the new app versions. Despite the urgency of fixing critical bugs, the rollout process can still be slow.