i think it is either SMIM (https://www.nexusmods.com/skyrimspecialedition/mods/659) or Skyrim 2020 Parallax (https://www.nexusmods.com/skyrimspecialedition/mods/2347) or a combination of the two.
Was having the same problem. I wasn't able to determine what was causing this, but I guess it's possible the texture is missing from the latest release of SMIM somehow?
Anyway, I was able to fix the issue with this: https://www.nexusmods.com/skyrimspecialedition/mods/21726
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Anyway, I was able to fix the issue with this: https://www.nexusmods.com/skyrimspecialedition/mods/21726