Gear VR dark line between separated edges

Hi Friends,

I got this bad problem on the separated edges between my models, I have the model here:

and the render problem in the editor here:

It is way more worse when I see it in GearVR headset, I wonder what is the cause of this particular problem, all my model are using unlit materials, shading were baked in VRay as texture completely, there is no light in the scene at all.

Thanks in advance!

JT