When I select 'adjust size and location' and then press 'OK' in the zoomed area, the zoomed area closes. (its size and location can be adjusted, but the picture-in picture zoomed area will not remain on screen. This behavior started after upgrading to Version 10.13.2, but persists with 10.13.3. My 2017 MBP 15" has two external displays. if that makes a difference