AO pass makes metallic materials black. WHY??

Sorry for low res… But i think the question is clear.
I can edit the AO pass in post of course, but i wonder what is causing it.

i just noticed, that the other metallic mats are are not influenced by the problem.

This material is in fact a combination of 2 materials.
I can show the node-setup later… im in a hurry now because the deadline is close. For now i have to edit the AO pass in post to get the job done in time.