mac wallpaper only covers a portion of screen while connects to external monitor

Hi Guys,

I use macbook that usually connect to a studio display. Studio display is set to main monitor, while the macbook is set as external display.

It was good and suddenly one day, when I unplug the macbook and then connects back to studio, wallpaper only show on upperleft quarter of the screen. Docs and files are showing fine just the wallpaper, I have to either adjust arrangement or change resolution to make the wallpaper showing normal.

How to fix this?