I've tried quite a few approaches to this but haven't been able to get a working solution.
On my laptop I noticed that the wifi 'sleeps' under screen lock which makes it impossible to leave it doing things that require an internet connection. For example: if a backup upload operation is running I would want to lock the laptop and leave it doing the upload.
I didn't see this issue with 15.10 so I'm guessing there's something either in device management or OS which I haven't figured out yet.
After spending a lot of time trying three different ways of turning off power management on the wireless interface I realised even that wasn't preventing the sleep.
For example:
sudo iwconfig wlp2s0 power off
Turns off the power management on the device until reboot but doesn't seem to affect the wireless-sleep-during-screen-lock feature. I've tried something similar with /etc/pm/config.d/wireless containing a script to do the same command as above but no dice.
Hibernate, sleep and suspend are all turned off and the laptop is a Surface Pro 4 i7.
I'm probably just missing something simple but can't figure it out. Any ideas?
Update 21-06-2016
This morning I've noticed that when a second monitor is plugged in it is ignored on wake / return-from-lock-screen. By unplugging and plugging monitor connection back in all returns to normal.
I think that perhaps somehow the two issues are linked.
Update 10-8-2016 Didn't get anywhere with the links I found in my comment below but found this clue in syslog:
NetworkManager[21369]: <info> [1470826457.2514] manager: wake requested (sleeping: yes enabled: yes)
I left my desk for 10 mins and when I returned I thought the wifi had stayed up. But no - it looks like it had resumed by the time I'd logged back in - perhaps the question here should really be
How do you turn off sleep and wake capability in Ubuntu 16.04.1?
As the standard UI (inc. Gnome tweak) tools & settings don't appear to achieve the right result, turning acpi=off has other consequences; what other safe methods are there?