Often when using multiple screens with a laptop then traveling away with just the single laptop screen applications my remember the second screen and disappear when windowed. Often you can “get them back” by maximizing the window.
A better method is to:
There’s a simple trick to get around this. First make sure you’ve alt-tabbed to the window, or clicked on it once to bring it into focus. Then right-click on the taskbar and choose Move
At this point, you should notice that your cursor changes to the “Move” cursor, but you still can’t move anything.
Just hit any one of the arrow keys (Left, Right, Down, Up), move your mouse, and the window should magically “pop” back onto the screen.
Note: For keyboard savvy people, you can just alt-tab to the window, use Alt+Space, then M, then Arrow key, and then move your mouse.