If you have a second monitor connected to your Windows 10 PC and are having issues with your application windows reverting to your primary monitor the potential solution for you to try below.
Click on your Windows 10 “Start” menu then type “Device Manager” and open it from the menu. From the Device Manager application menu select “View” then “Show hidden devices“. The device listing will then update. Scroll down and click on “Monitors” to expand it. Right click on any greyed out monitors and select “Uninstall device“. A reboot at this time is recommended after which this should no longer be an issue. Note, if this doesn’t work you may try simply uninstalling all connected monitors (do not uninstall anything else, such as your graphics card driver) and restart your PC.