Same issue. Chromecast was working fine as recently as a few days ago, now cannot connect when I try to cast on any of my devices. I have three Chromecast-enabled devices on my network and I cannot cast to any of them. The one I deleted from Google Home and attempted to re-set up won't complete the setup process; the other two are still showing as connected (both in Google Home and on my router's table) but won't accept a cast request.
I called Google. same thing. its your router. I went to 10.0.0.1 -> Advanced ->Device Discovery -> Zero Config and Enabled That. Restarted the router. And, the chromecasts are now showing up. and, am able to cast to it