When I drag the ProjectLibre application window to a second/external display, the window turns black - this is true when the laptop's display is the primary display.  Am running Windows 10 on an HP Zbook.  Both the laptop and external display are set at a resolution of 1920 x 1080.

Work-around:

If I configure the external monitor/display to be the primary display, then ProjectLibre application window appears as expected no matter which display the window appears on.