Of course, when I invert the Y or the green channel it changes but as I said earlier, one mesh will still remain incorrect: I invert the Y in the common "aiNormalMap" node to correct the mesh on the left, then it becomes correct while the mesh on the right becomes incorrect. And when I change tangent space handedness…
You were right, poopipe, UVs are flipped. At first it just seemed strange to me that they could be flipped while only normal maps were working incorrectly. And even if they were flipped, I wouldn’t even think that it may be a problem for Maya. But after you wrote that you weren't sure how Maya works with flipped UVs, I…