screen lock cycles screens on/off constantly

Both my home and work machines, running Ubuntu Gnome 16.04, both fully up to date suffer this issue. I check both machines for updates daily in a hope for a fix to this extremely bothersome issue.

The machines both have external monitors, and if I lock the screen with Win+L the screen will lock then sleep. A few seconds later, when the external monitor goes into "sleep" mode, the computer decides to "reconfigure" the connected displays (as happens when you unplug a display physically) and the screen is woken again for a few seconds, the screens and computer will then shortly thereafter return to sleep, monitor switches off and the cycle starts all over.

This alone is annoying but not the worst issue. At work this causes all 3 of my screens to switch on and off every few seconds which is annoying for my colleagues if I'm away from my desk, and at home this results in the music, playing through my monitor-connected speakers to start/stop constantly as the monitor goes on and off.

More importantly, once I log back in, gnome-shell is totally unresponsive and I have to restart it with CTRL+F2, r then performance returns back to normal, usually I'll see a bug report dialog if I've left it long enough (say gone out to lunch).

I can add that if I use a "dumb" monitor over VGA for example and no other external monitors, there is no "sensing" occuring so the problem does not happen, sadly, most of my monitors are HDMI/DP.

Both machines are laptops and do NOT suffer the issue if NO external displays are connected.

It seems to me the bug is that the computer shouldn't "reconfigure" displays when the screen is sleeping and thus wake itself.