Hello,
Not really a problem, but just wondering if this is a known issue…
I have a Chromecast Ultra and a Chromecast Audio. Arround 4 AM the Ultra goes to the state unavailable and returns immediately back to the state off. Arround 4.30 AM samen thing with the Chromecast Audio.
And this every day…any idea ?
Sounds like router/network thing.
Do you have any other devices that you could look at if they drop communication also?
I actually discovered it by accident (automation that turns on my receiver as soon as the chromecast status is other than ‘off’).
Both chromecasts are located half a meter from the router and are directly connected to it. If they both had this phenomenon at the same time, then I would indeed be thinking of a router or connection problem.
But since this isn’t the case, I was thinking more towards a built-in small daily reset in the chromecast itself.
I followed your suggestion, I will monitor 3 other devices on my network…we will see tomorrow if the state changes 
I know some countries have (or at least had) a requirement that routers would restart every day in order to get a new external IP.
Not sure if this is still a thing but I know a few friends who had that issue.