Google Nest Community

Set the date on your phone to before 7th March and set up your device(s). Then you can change the date back and everything should be back. It's a pain but it works.

I tried that but unfortunately it didn't work for me. 

Yeah, it's just a shame I've reset all 4 of my Audio's. At least I still have the Mini to use until (if) it gets sorted out. It was nice to be able to wander around the house and have the sound synced in every room...

I've tried that and unfortunately I still get the same "Could not communicate with your Chromecast Audio." 

I wouldn't mind so much if you could still get the audio only Chromecast, I bought the second two when they were discontinued. I've had them quite a while and don't expect anything to last forever, but...