Over-shaded surfaces where it's supposed to be white but turned reflective black.

Hi all,
there is this weird thing happening on my scene which i have no idea how to solve it after spending half a day trying to troubleshoot whats going on.
Ther surfaces,circled in red area meant to be the same material as the rest of the wall/ceiling. That being said, they should be white. Initially they are showing fine, but after some more lights being added to the scene, i try to rebuild the lighting and it became this shaded/unlit/ reflective black…

I’ve tried stuff like material matching all the surfaces, hiding the additional lights and rebuilding them again but it just doesnt work. Btw, they are detached box meshes from the main model. The funny thing is, the material are white again when i move them out of their location. Any clue? I’m still new to unreal… only 1 week old to be exact…

Global Settings that i’ve changed>
Num Indirect lighting bounces 100
Environment colour to white
Indirect lighting smoothness 0.6

Thx in advance for helping out!

Attached is close to how i wanted it to look like ( i ‘fixed’ it after altering the position of the walls by a bit, it will still be black after being built).

any helppp? =(