Why does the texture change over connected UVs?

I made and unwrapped this deck chair in C4D and imported it to UE4 as an fbx and textured it. I’ve been through this process several times without issue and I understand the ins and outs of UV mapping without overlaps etc.

But for some reason the texture of this model changes in brightness from one UV polygon to the next, even though those UV polys are totally connected and look fine in C4D. You can see an example of this on the top of the arm rest at the ends. Ignore the fact that the texture is low res, I know how to fix that, I just don’t understand why the brightness is changing between connected UV polys.

The problem was “Normal Smoothing”
I have no idea how to affect the normal smoothing in C4D but I was able to open my model in blender and correct the issue by unchecking this radio button called “auto smoothing”:

220851-screenshot-615.png