https://raspberrypi.stackexchange.com/questions/94178/wifi-wont-start

sudo killall wpa_supplicant
sudo wpa_supplicant -c/etc/wpa_supplicant/wpa_supplicant.conf -iwlan0

--> Autostart-Script: 
etc/rc.local abändern und code aus obigem Link einfügen!

Danach Konfiguration der Wifi-Setting: 
* "Wireless and Wired Network Settings"
* Interface
* wlan0
* Aktivieren: "automatic configuration" && "disable IPv6"
* Alle Felder leeren