Normal map bug - stripes on the image when parallel with light source

Development Asset Creation FX
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1

I have plane with normal map 0,0,1 color.
Whenever I set it in parallel with light source I see this wierd stripes.

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image1280×904 60.9 KB

Why this is happening?

If I use Two Sided Folliage then I get this even without normal maps

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image1493×1197 73.6 KB