Network Manager frequently disconnects wlan0

[Francis Watt]

In syslog there are multiple lines: wlan0: CTRL-EVENT-DISCONNECTED reason=4 locally_generated=1

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: network-manager 0.9.8.8-0ubuntu7.3
ProcVersionSignature: Ubuntu 3.13.0-117.164-generic 3.13.11-ckt39
Uname: Linux 3.13.0-117-generic x86_64
NonfreeKernelModules: fglrx
ApportVersion: 2.14.1-0ubuntu3.23
Architecture: amd64
Date: Wed Apr 26 16:56:26 2017
ExecutablePath: /usr/sbin/NetworkManager
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 auto lo
 iface lo inet loopback
InstallationDate: Installed on 2016-08-27 (242 days ago)
InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
IpRoute:
 default via 192.168.1.1 dev wlan0 proto static
 192.168.1.0/24 dev wlan0 proto kernel scope link src 192.168.1.3 metric 9
NetworkManager.state:
 [main]
 NetworkingEnabled=true
 WirelessEnabled=true
 WWANEnabled=true
 WimaxEnabled=true
ProcEnviron:
 LANGUAGE=en_IE:en
 TERM=linux
 PATH=(custom, no user)
 LANG=en_IE.UTF-8
SourcePackage: network-manager
UpgradeStatus: No upgrade log present (probably fresh install)
nmcli-dev:
 DEVICE TYPE STATE DBUS-PATH
 wlan0 802-11-wireless connected /org/freedesktop/NetworkManager/Devices/1
 eth0 802-3-ethernet unavailable /org/freedesktop/NetworkManager/Devices/0
nmcli-nm:
 RUNNING VERSION STATE NET-ENABLED WIFI-HARDWARE WIFI WWAN-HARDWARE WWAN
 running 0.9.8.8 connected enabled enabled enabled enabled disabled