I have a Pioneer VSX-103 receiver that has Chromecast built-in. It was working just fine, and then one day it stopped working with my speaker groups, and my Home app showed the device offline, just like in the article linked below. I attempted several of the troubleshooting steps others performed, and ended up trying to remove the device from my home. Upon doing so, I was no longer able to get the device to re-add to my home. The step that finally worked to do this was to create a new home, in which the Stereo showed up without me adding it. I was then able to add the stereo to a room in my original home. Upon doing so, I am able to get the stereo to play, but the device shows offline in the app. It appears there is still something broken in the google home app. Just wondering if anyone else is experiencing this or if this is possibly a known issue that google might be still looking into.
Thanks for sharing details about the issue here. Please note that we have very limited support on third party speakers with built-in Chromecast like Pioneer. Since basic troubleshooting steps has been exhausted, I suggest that you reset your device then set it up on the Google Home app. If this doesn't work, please contact Pioneer Support for further assistance.
@MikeClark: Thanks for helping here!