Problem: During initial setup, Rachio 3 connects to WiFi network (solid light 2) but fails to contact Rachio cloud (white blinking light 3 with occasional red blink). My router shows no Rachio device is connected (this contradicts solid light 2).
After many reboots, about 6 hours of self-debugging and 4 fruitless calls to tech support, I finally got it to work.
Solution: I changed my router authentication setting from WEP to WPA. This required me to add all my devices back to my network. When I tried the Rachio again it connected just fine. Not sure what was causing the issue, but it seems like changing from WEP to WPA fixed it for me.
Hope this helps someone!