Static object doesn't receive the emission material's lighting.

Hi guys, I just tried out the emission material inside the unity.
The room is simply planes and the light source is a plane with emission material.

The first time I tried to use the emission light material it worked(all the walls are checked static).
There are some problems obviously but it looks just fine. (As shown below)


However, I don't know what's going on, after several rolls of adjustment and rebaking, the wall just became totally black.


I checked out the baked lightmap on different walls and they're all black.

Then I tried to create the new scene and redo what I previously did to ensure there's no setting problems and even built a completely new project with the exact same way of the first time I did on the emission map, but they just didn't work out. I even start wondering whether this is my CPU issue.

Hope can receive some suggestions here.
Thanks
Kai