There are several ways to fix this without needing to be aware of the window's off screen position.
- From the keyboard WIN+{Left|Right} resizes and pins the window to the side of the screen
- From the keyboard WIN+Up to maximize the window (or right click on the task bar and select maximize. Now, drag the title bar from the top and the window will unpin from the screen and move with the mouse
- Right click on the task bar and choose any of the windows arrangement options (Stack, tile, cascade)
- select non-maxmised open window
- keyboard shortcut Alt+Space. Then M. to move.
- use arrow keys to move windows offscreen, say to the right. Don't touch the mouse!
- Hit Enter key to confirm position.
From now on. Anything but "full maximise from the taskbar" makes the window "disappear" without a trace. "Restore" from the taskbar doesn't help.
And assuming you even know exactly happened, you still have to guess which direction they took the window and how far...
How is it there is no "Position Reset to 0,0" option?