I have no apps that have access to the sound output. The problem persists even if I run ONLY Chrome.
I am not the only one - you can see such an issue on the Chromecast support forums for many users. I have tried all recommended solutions like media router enable/disable etc. including using the Canary version. No luck! I have also raised this with the Chromecast support team like 2 weeks ago. I haven't heard from them since then.