Best answer by Stanley_4
Search string: site:en.community.sonos.com Can't add songs to queue
Gets you: https://duckduckgo.com/?q=site%3Aen.community.sonos.com+Can%27t+add+songs+to+queue&ia=web
I'd start with a reboot of the router too, if that doesn't do the trick unplug your Sonos gear, reboot the router again, reboot your controllers and then power up your Sonos gear one at a time, wired and then closest to the router, about a minute apart.
One or the other should get you to where you can at least submit a diagnostic.