Since Cyan , my lumia 1520 occasionally fails to connect to known wifi access points like my home acess point. I havent been able to confirm a pattern yet, but in most cases a restart is required, or having to manualy reconnect by going to the wifi settings.
Today for instance the router restarted, and all my devices reconnected except the lumia. Going to the wifi settings, the network was visible and listed, just no automatic reconnection.