Lockscreen doesn't turn off the screen

[lunix]

Lockscreen doesn't turn off the screen (saw it via Bug # 1292041 now closed)
Ctrl=Alt+L or Super+L shortcut works and blanks the screen
requiring me to type my password again to activate session.

However my System-Settings -> Brightness & Lock is set to:
Turn screen off when inactive for: 30 minutes
Lock: OFF
Lock screen after: Screen turns off (is grayed out)
Require my password when waking from suspend (unchecked and grayed out)

I have dual monitors. Both are Samsung and this feature is highly
intermittent, meaning sometimes it works and often it doesn't.
For example it hasn't worked for days but I changed the System-Settings
from 30-minutes to 1-min. and it started working without a reboot.

Is it possible that a kernel update changes some value that alters the
setting? Then when I change the time in the window it repopulates a value?

I am on Ubuntu 16.04.1 but I have seen this issue for years now.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[fugounashi (fugounashi+launchpad)]

This bus is present in 16.04.

Single monitor
System Settings, Brightness and Lock, Turn screen off when inactive for: 10 minutes.

dpms activates after 10 minutes of inactivity

activate Lock from menu or Ctrl+Alt+L
dpms never activates

[Digulla-hepe (digulla-hepe)]

Duplicate of Bug #1292041