You are plugging the red channel of the diffuse into the strength of the SSS, which make the SSS multiplier entirely dependent on brightness red channel in the diffuse texture. Every face texture will have a different multiplier when doing that. Your SSS scale is to high, needing 10 times reduction. 

Basically, your blowing the SSS up. Cycles averages around 0.003 to 0.03 for scale (subsurface in the principled node).

If 0 is black, and 1 is white, 0.003 to 0.03 is a very dark color.

Your basically using 0.3-0.4, which is about 10 times to much on the max side......

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