I don't know, if anyone else got this problem, but Chromecast just stopped working for me. I had a little rule, where I would use chromecast as my alarm, but for some reason, it never started. Re-Wrote it quick to test if the Nest Hub is the problem, but it doesn't work with the Nest Mini either.
Mine stopped working when I accidentally cut power to my router. When it rebooted, it must not have picked up the GH-Mini as speech wasn't working. I unplugged the mini and rebooted it. Then on the device page, hit the Intialize button. After that, I set the volume and sent a test message. It worked then. If you haven't tried that, perhaps it will help.