Over the years, I have come to the conclusion that unless an app explicitly specifies which monitor a window should appear on (eg, restoring coordinates persisted when the app was last closed), it'll default to the monitor where the mouse pointer happens to be on by the time it's ready to be shown.

Is there any truth to this, or is that just my imagination?  I definitely have some apps that make no effort to try to remember where they last showed up, and they consistently"follow the mouse" in this fashion.  Others...not so much.  So to this day I wonder whether this is behavior inherited from Windows itself or not.