Actually, i have a similar issue, but with AO.

AO is set on the character skin and on the cloth.
The strap and the cloth are separate material channels.

On the left pic, no transmap, only plain cloth. The AO is visible on the skin.

On the right, a transmap is applied on the cloth material (not on the strap). The AO is visible on the skin ONLY under the strap, NOT under the cloth.

Is it a known issue with AO?

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