I have 3 Chromecast devices and 1 Chromecast Audio.
The Chromecast attached to the TV at the main router is very stable and rarely gives is problems.
One of the other Chromecasts has to be powered down when that TV is not in use so on each use it has to go through a restart. On Saturday I noticed that even after a restart I couldn't find the device. The Chromecast backdrop photos were scrolling, it showed up on startup as connected to the network but it was not visible in the apps or in Home. It took a restart of both my mobile device and the Chromecast to get it working. This issue was with a Samsung S7.
Today (Sunday) I was trying to use the third Chromecast and had similar issues except, at times, the Chromecast was visible in Home but not in the apps (Netflix or Google Music). Again several restarts of both Chromecast and mobile device were required. Eventually I got it working but after watching a feature film the Chromecast disappeared from both Home and the app (Netflix). The film credits were rolling but I could not stop the film or choose another film. These issues were with Samsung S7 and S5. The S5 was unable to see the Chromecast. Both mobiles are up to date with software.
I get similar issues with the Chromecast Audio but to a lesser extent.
I am beginning to have severe reservations about Chromecasts reliability.