I’ve found as long as you select the window, use the keyboard shortcut to select move as you noted, use the arrow keys to move it a few steps, after that move the mouse without clicking and the window often moves with it at that point.
But yeah it’s the side effect of an inbuilt setting to remember last location on screen when the app was last used. Just not taking into account that the specific screen location is no longer available.
Ah man. Now I’m gonna have to pull out the ol red alert 2. The only game I’ve played where 10 hours just disappeared. Started just after breakfast and next thing I realise, everyone in the house is fast asleep and it’s pitch black outside.