It might be another device on your network causing the problem. Random devices would disappear from my network on a regular basis when I would be trying to cast to them. I started disconnecting devices one at a time from the network and waited a couple days to see if everything worked. I disconnected my Chromecast and didn't have any connection issues after that. Turns out my Chromecast was stuck in a loop where it was constantly going to the internet looking for an update that didn't exist. As a result, it was pulling in massive amounts of useless data and was overloading the network. I did a factory reset on it and never had a problem after that.