I have the same issue with my CR700 modem router. Worked great for about 4 months, then a couple days ago started losing WiFi connection to every device in the house (Echo, Nest, Roku, etc...)....

I loose WiFi connection to every device in the house (Amazon echo, Nest thermostat, roku, etc). I unplug for about 10 sec and back to normal for a little while. This just started a couple days ago....