Test case Attached.
Primary monitor(screen0) 192DPI
Secondary monitor(screen1) 144DPI
When the frame is on screen0: works as expected, created screenshots contain the frame.
when the frame is on screen1: created screenshots do not contain the frame.
It could be because the screenshot method uses scale 2 as on the first screen instead 1.5 that is actual scale on the second screen. So the region where the screenshot is taken is shifted.
On Linux: Not Tested.
On MacOS Sierra version 10.12:
Tested dual monitor setup with primary Retina display and connecting a secondary monitor non-Retina display. keeping secondary monitor to the right/left of main display and targeted rectangle on each sides, expected results are obtained.