I'm unable to connect to a saved hidden wireless network.
As suggested here (https://bugzilla.gnome.org/show_bug.cgi?id=639336#c3)
I've opened this, a new, bug report in order to advise NM team about this big bug and help you to solve it.

Description:
NM is not able to connect to a saved hidden wi-fi network;
the saved network doesn't appear in the available networks menu (gnome-shell -> Select Network) so I can't choose it AND  also using the gui (Wi-Fi Settings -> Connect to hidden network... -> (I select the hidden network from the drop-down menu) -> Connect is grayed out)

the workaround (caught somewhere on the web): execute this command `sudo iwlist ABC scanning essid XYZ`; in this way NM, seeing magically the known network, connects; where ABC is the wireless adapter and XYZ is the hidden network's name

Software:
- Arch Linux x86_64
- gnome 3.20.2
- networkmanager 1.2.2

Steps to reproduce:
- add the hidden wi-fi network and mark it as `automatically connect`
- reboot
- NM is not able to automatically connect to the saved hidden wi-fi network