Xfce4-power-manager display blank, suspend and shutdown no longer works

xfce4-power-manager ignores display settings. The settings are:

/xfce4-power-manager/blank-on-ac 10
/xfce4-power-manager/dpms-enabled true
/xfce4-power-manager/dpms-on-ac-off 12
/xfce4-power-manager/dpms-on-ac-sleep 11
/xfce4-power-manager/inactivity-on-ac 120
/xfce4-power-manager/power-button-action 4
/xfce4-power-manager/show-tray-icon false

System suspend works fine but Display blank, suspend and switch off do nothing.

This started a few weeks ago after having worked perfectly for many years. I have tried all of the typical trouble shooting methods such as: xfce4-power-manager -q;xfce4-power-manager --no-daemon --debug. But I can see nothing in the output that is useful. I have also deleted the per-channel config file from a tty after a system restart and then reset the configuation from the power manager config gui. Still no luck.