Same here, suddenly this morning after restarting the arduino IDE the ports section was greyed out on Ubuntu 16.04. Tried all kinds of stuff, no success. Finally found this thread and disconnected the network connection.
Boom, all ports are back. WTF is this?
uninstalled the modem manager, but no change.
Once arduino is started i can reenable the network connection ann everything works fine, even new ports are detected then.