I needed a fresh start on my laptop (a ThinkPad T440S) and thought I would try starting with Ubuntu Server 16.04, so I can install what I want without as much Ubuntu Desktop bloat.
For networking I installed network manager and it’s corresponding tray applet control application (the network-manager and network-manager-gnome packages, respectively). Everything worked great, except that 5Ghz networks weren’t showing up to connect to.
I don’t recall where I found this solution, but the answer was to edit the file /etc/default/crda, which had this line
REGDOMAIN=
This needed to be changed to
REGDOMAIN=US
Saving that change and rebooting fixed the issue – it’s possible that restarting network services might have done the same as the reboot.