Mirroring and stacking UVs leads to tangent discontinuity and seam

Question

In Maya I have a mesh where I mirrored the top half of the geo, which also mirrored and stacked the uvs. I did this to increase texel density. I then exported as a .fbx file and made sure to export smoothing groups but not tangents and binormals. Next I imported the mesh into Substance Painter and checked the box to "compute tangent space per fragment"

I didn't bake, but just applied a brushed metal material (not even a smart material). I see very visible seams where the geo was mirrored, please see the screenshot below:

Here is the uv layout in Maya. The checkerboard pattern is aligned so I would think the pattern should be contiguous:

Could it be related to the filter?

TimothTy · Answer

I ended up trying to solve this in Unreal Engine 5. I brought in my plane  mesh with the texture and sure enough the seam was there too. Based on this thread: https://polycount.com/discussion/116922/a-solution-to-normal-maps-with-mirrored-uvs-in-udk I flipped the x channel in a shader just for the mirrored uvs and the seam was gone! I'm guessing Painter doesn't do any kind of auto flipping of vectors for mirrored shells? (I tried a plane where the mirrored axis was x instead of y like the image in my opening post)

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