Monitors do not turn off (enter powersave mode) after screen blanking
Solution 1:
WORKAROUND
Change the setting of your monitor from input select: auto to a fixed input, e.g. hdmi.
Here, with a AOC Q3279VWFD8 (WQHD):
OSD -> extra -> input select -> hdmi (was auto)
That fixed my problem, also that setting prevented my other monitors from entering powersave mode (turning off). It seems a monitor can poll the graphic card through HDMI (CEC?), preventing powersave mode. Probably cable type plays a role as well.
Still I consider this a bug, IMHO powersave mode should work with default settings of monitors.