Hi anyMOTION GRAPHICS,
Please share a scene file, reduced to the problem. If you have problems to upload one, I can set up an Upload link. Please with two images that shows the problem.
With the current build, Hair needs to be based on polygons to do the trick, as in Hair>Generate>Type—>e.g., Square or Circle. If the Physical Renderer is used, it internally changes this to polygons automatically.
AO is a calculation of angles between surfaces. An old fake to get some kind of GI fake in it. It does not represent any light source. Since Hair is in Standard Render not based on polygons by default, I do not expect to show anything “hair” in the AO pass. Since the surface of an hair can change and is perhaps even partially transparent, this “angle” can’t be determined, hence the need for something like a geometry. Like in specific render-modes hair is always turned into “virtual-polygions” during rendering.
I have captured a one minute clip to showcase the difference some settings have with the current build: (Just a quick impression, not meant to be at all more than that)
https://www.amazon.com/clouddrive/share/qcBsrwilaieUYocnds4sWHBhugoH6pOOK9A9cLWPMfz?ref_=cd_ph_share_link_copy
If you find that there is something that should work differently, please contact the support:
http://www.maxon.net/support/support-questions.html
All the best