Hi,
I have the exact same problem as the OP. Used to work fine but now doesn't.
I've got a Galaxy S7 (SM-G930F, European Exynos version). Android version 7.0, kernel 3.18.14-12365438
Regarding the Chromecast, I am not part of the Preview programme and have never been, but my Chromecast Audio has been updated to firmware 1.30.111140
I also have a Chromecast 2. This is firmware version 1.29.104827. It works fine.
I don't know why my Chromecast Audio has picked up the preview version, unless it has become the release version and Google has not updated their information page:
https://support.google.com/chromecast/a ... 4014?hl=enBy the way; I can work around the issue by use the "Cast screen / audio" function in Google Home. That seems to eat more bandwidth and be less stable than casting directly from Neutron.