How to Load Small Cell in World Partition Window

Hi,

I am exploring the world partition recently. I found out that somehow the cell in the world partition window became a whole cell instead of a small individual cell. I can only load and unload the whole world and when I unload the world, I cannot reload it again.

You can see that in the world partition window. This is one square grid. It will be loaded and unloaded as a whole. But in level, it seems to load the small grid based on the distance. I cannot select the small grid inside the world partition window. Does anyone know how to fix this?

Thanks for your reply.