Hello reporttheloss,
What kind of display setup are you using? What are the resolutions of these two monitors? How are they connected? Is it through Display Port, HDMI, DVI etc.? Are both of the monitors connected to your GTX 1080 or is one on an integrated graphics card?
Have you used a previous version of the engine where this doesn’t happen or was 4.12 your first one? I would be interested to know if this is version-specific or not.