We have this problem at job right now. The normal has square like artefacts. It’s from painter so it might be their problem, I will ask them help as well as here.
You might have some smoothing issues with the original mesh that the normal map was baked from. Also make sure your normal map is set to use Normal Map compression.
There is only one smoothing group, we tried normal modifier then flip back the faces to be sure, Normal compression too, still the same result.
The artefacts do not follow the topology of the high res model.
Here more screenshots
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