My materials change colour on box brushes

This is my first post here and I am still very new to UE4 so I’m not super good with all the terms and I apologise if this is in the wrong catagory.
My current project involves me using box brushes to construct basic buildings and everything is going well enough. However the material I’m using on the box brushes changes and I cannot figure out why.

Oftentimes I will place a material on one face of the brush and then place the same material on the opposite face, however one will be significantly darker than the other. This occurs even though both faces have equal lighting. I have tried different materials from different material packs but the issue still persists.

Is there an explanation for this or is there any way I can resolve this?