This occurs if you re-size your browser window , while you have a landmax window open.
There are a number of options you can do:
- Double click the header of the window, and it will match the screen size.
- Make your browser full screen and then close the window
- On the task bar on desktop - you will see a tab for the window - right click and options to close the screen will appear
The window resizing for Chrome on Windows, should work if you do a quick double click on the Tab.
See attached screenshot.