Comment 4 for bug 1394204

I see lots of these messages:

Nov 19 08:03:43 ubuntu-phablet NetworkManager[1448]: <warn> Activation (wlan0/wireless): association took too long, failing activation.
Nov 19 08:03:43 ubuntu-phablet NetworkManager[1448]: <info> (wlan0): device state change: config -> failed (reason 'SSID not found') [50 120 53]
Nov 19 08:03:43 ubuntu-phablet NetworkManager[1448]: <info> NetworkManager state is now DISCONNECTED
Nov 19 08:03:43 ubuntu-phablet NetworkManager[1448]: <warn> Activation (wlan0) failed for connection 'Canonical-5GHz-an'
Nov 19 08:03:43 ubuntu-phablet NetworkManager[1448]: <info> (wlan0): device state change: failed -> disconnected (reason 'none') [120 30 0]
Nov 19 08:03:43 ubuntu-phablet NetworkManager[1448]: <info> (wlan0): deactivating device (reason 'none') [0]
Nov 19 08:03:43 ubuntu-phablet kernel: [51481.120852] wlan: [1317:E :SME] csrMoveTempScanResultsToMainList: 2908: 11d AP Bssid 84:18:3a:44:da:ec chan= 36, rssi = -50, countryCode US
Nov 19 08:03:43 ubuntu-phablet kernel: [51481.121920] wlan: [1317:E :SME] csrMoveTempScanResultsToMainList: 2908: 11d AP Bssid 84:18:3a:44:da:e8 chan= 8, rssi = -40, countryCode US
Nov 19 08:03:43 ubuntu-phablet kernel: [51481.122835] wlan: [1317:E :SME] csrMoveTempScanResultsToMainList: 2928: Information about current country Bssid 84:18:3a:04:da:e8 chan= 8, rssi = -40, countryCode US
Nov 19 08:03:43 ubuntu-phablet wpa_supplicant[1828]: wlan0: Failed to initiate sched scan
Nov 19 08:03:43 ubuntu-phablet wpa_supplicant[1828]: wlan0: CTRL-EVENT-SCAN-STARTED
Nov 19 08:03:44 ubuntu-phablet kernel: [51482.020195] wlan: [1317:E :SME] csrMoveTempScanResultsToMainList: 2908: 11d AP Bssid 84:18:3a:08:65:b8 chan= 4, rssi = -84, countryCode US
Nov 19 08:03:44 ubuntu-phablet kernel: [51482.021142] wlan: [1317:E :SME] csrMoveTempScanResultsToMainList: 2908: 11d AP Bssid 84:18:3a:44:da:ec chan= 36, rssi = -50, countryCode US
Nov 19 08:03:44 ubuntu-phablet kernel: [51482.021935] wlan: [1317:E :SME] csrMoveTempScanResultsToMainList: 2908: 11d AP Bssid 84:18:3a:44:da:e8 chan= 8, rssi = -38, countryCode US
Nov 19 08:03:44 ubuntu-phablet kernel: [51482.022912] wlan: [1317:E :SME] csrMoveTempScanResultsToMainList: 2908: 11d AP Bssid 84:18:3a:04:da:e8 chan= 8, rssi = -37, countryCode US
Nov 19 08:03:44 ubuntu-phablet kernel: [51482.023614] wlan: [1317:E :SME] csrMoveTempScanResultsToMainList: 2928: Information about current country Bssid 84:18:3a:04:da:e8 chan= 8, rssi = -37, countryCode US
Nov 19 08:03:45 ubuntu-phablet NetworkManager[1448]: <info> (wlan0): supplicant interface state: scanning -> disconnected
Nov 19 08:03:45 ubuntu-phablet NetworkManager[1448]: <warn> Couldn't disconnect supplicant interface: This interface is not connected

It tells me you're likely just outside of the range of the accesspoints, and since it comes in and out of scan results regularly, NM will keep trying to authenticate while the AP is available.

A couple of things to try:
 - Switch to 2.4GHz, see if the behavior is the same, this could give us some interesting data points.
 - Disable location, which causes significantly more wifi scans to be triggered, and reducing that may also improve the situation.
 - Try to attach strace to NetworkManager and/or dbus-daemon, this would let us see what they are spinning at when they are consuming lots of CPU (as per the report).