Staged rollout of new firmware with the fix started today.
And here:
www.googlenestcommunity.com
And here:

Re: Regarding an issue with Chromecast 2nd gen and Chromecast Audio
Hey everyone, thank you for your patience while we work to resolve this issue. Here’s the latest: We have started to roll out a fix for the problem with Chromecast (2nd gen) and Chromecast Audio devices, which will be completed over the next few days. Your device must be connected to receive...