We've had this Chromecast Ultra working fine for a couple years, and use it for all TV-based entertainment so we've streamed through it from many different services.
A few days ago I noticed that a soccer game I wanted to watch with NBC Sports via Chromecast didn't have audio, but video worked fine. I assumed something was wrong with the speakers and ignored it figuring I would investigate later.
Later in the day I was casting something from HBO Max which worked fine, so I thought the issue had resolved itself, but then when casting from YouTube I had the same problem, video but no audio.
We've tested streaming with several apps now, including ESPN, Hulu and Netflix, but they all have the same problem, no audio.
HBO Max continues to work fine though, so I don't know what's going on but I don't think it can be a configuration issue.
I also recently have connected a Stadia controller to this Chromecast so maybe that's causing a problem?
We've rebooted this thing and just factory reset it but nothing has worked.