Normals are well… normal but when I import the mesh into studio This face is always missing. No modifiers but shade smooth is on.
Have you tried to enable double-sided in the appearance section of properties?
Have you done a clean up → merge by distance on it before exporting? Sometimes a double can be hiding where you least expect it.
Please don’t suggest this as a fix for broken meshes.
If the mesh isn’t correct and you use DoubleSided then the shading will be affected, giving light and dark spots because you’ve used a side that’s not oriented correctly.
@Iagtrap did you possibly mess up on the Texture and miss that Face? It’s hard to tell from the Blender screenshot if we are looking at the correct edge because the Studio screenshot is much closer and the orientation seems to be from a different side. Also the brim of your Blender image seems to be a squared off edge, but the Roblox image seems to have a bit of an angled deflection in it as shown by the shading.
I seemingly also had this problem when I separated and filled multiple faces together, I’m guessing it’s an issue with faces not being connected properly.