I have an Asus RT-AC66U router and a MacBook pro 13" early 2015. Ever since i installed El Capitan i have a problem with the 5 GHz band. If the 5 GHz is primary and i start up the Mac it cannot find the WiFi signal. When i make the 2.4 GHz primary there is No problem when starting up and instantly there is a good connection. I then can switch to 5 GHz without any problem. I hoped that the update yesterday would solve the problem but iT did not. I begin to wonder if the problem can be found in the router setting. Does anyone has an idea?