I am sorry, here are some images illustrating whats going on in the scene.
You can see the planes are basically stuck to the wall, overlapping just on the edge of the paint peels with the wall surface.
On the other hand, in the mesh details panel I checked both two sided Lighting and Two sided shadow, but still got this lighting bake result… no shadow casting from the wall peels planes…
I hope this is useful to make it easier for you to help me. And really thank you to anyone who helps :)!