Since a while i couldn't connect via netctl to a wireless network. But since a manual connect like this worked:
wpa_supplicant -B -i wlp4s0 -c <(wpa_passphrase "my_ssid" "mypassword")
I didn't bother too much. Today I read through the documentaion again and found a suggestion if the connection fails.
I added this line manually to /etc/netctl/my_profile_name
ForceConnect=yes
And a sudo netcl start home was successful \o/ I removed the line again and it still woks, strange but who cares.