Because we don't know what your model looks like (preferably low with the AO tex on and a shot of the highpoly) it's harder to guess.
You may want to visualize the rays used to calculate AO as hairs growing out from the mesh and wherever the hairs touch, they make it darker. My guess would be that no "hairs" are touching that section of the mesh and the actual issue is with the surface underneath that white swatch which may be getting more ao than it should, probably due to fucked up normals.
It's hard for anyone to say without seeing the high-poly/lowpoly.
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You may want to visualize the rays used to calculate AO as hairs growing out from the mesh and wherever the hairs touch, they make it darker. My guess would be that no "hairs" are touching that section of the mesh and the actual issue is with the surface underneath that white swatch which may be getting more ao than it should, probably due to fucked up normals.
It's hard for anyone to say without seeing the high-poly/lowpoly.