It looks to me like the normal became flipped on that face. I can’t be sure from the angle though.
try triangulating your mesh
Triangulating the mesh does work, but it adds too much complexity to my model. I,m trying to keep it low poly and super simple.
Here’s a picture from another angle of the same model to better see the direction of the normal.
Looks fine to me.
I wonder what is causing this. I made another model and it keep creeping up in some faces.
game engines use triangles anyways