Hello Michael,
Thanks both for getting back and trying to resolve the problem.
I checked the render counts and put the same counts number on both in every modifier. I just re-rendered it, but I had the same result.
Vray RT takes in account every modifiers in the stack so it works in RT.
But I have the strong feeling that in production mode, Vray is stuck on the first "Hair from guides modifier" hairstyle.
Let me explain my process from zero to problem (screenshots below):
step 1- I'll be processing by steps. I did the first "Ox Edit Guide", stylizing the hair straight, with straight fringe and backhair, to ease the process of hairstyling (like hairdressers do?). Then added an "Ox Hair from Guides" to add 300 individual hair (I called it "Ox Hair 300 from Guides"). (second screenshot: you can see in the viewport).
step 2- Then, I add another "Ox Edit Guide" on top of the first "Ox Hair 300 from Guides" then readjusting the hairstyle a little more to acquire a more precise hairstyle, breaking the fringe and having some backhair on the shoulders and sideburns going backward, stranded behind the ears. Then I add another "Ox Hair 500 from Guides"("500" for 500 generated hair).
step 3- I add another "Ox Edit Guides", stylizing a bit more the hairstyle. Again I add an "Ox Hair 3k from Guides" modifier (3000 hair).
step n- Et cetera. Until I get to thousands of hair with the right hairstyle.
But when I render the scene to test the hairstyle, I get this odd result I have shown you in the screenshots. I noticed huge differencies. In the render, I recognized the very first "Ox Edit Guides" hairstyle (from step 1) because of its fringe and backhair going straight to her back (and not showing hair on the shoulder, for example, like modeled in the viewport [see screenshot 1]). This was the only step I did it to get a straight look before brushing it later. You can see it in screenshot 2.
That is why I think the render gets stuck to the first "Ox Hair from Guides" modifier...
screenshot 1 = Rendering the scene with the hairstyle shown in the viewport. Note how the hairs on the shoulder aren't there, featuring this f* ugly fringe as well:

screenshot 2 = Comparison between last render (from the screenshot above) and the viewport hairstyle with only the first "Ox Hair from Guides" modifier activated... quite similar! :

I don't know if how I processed it was the right approach, but I think it is quite a clean workflow as I evolve through my hairstyle, detailing it with steps (Hair from Guides). I wondered how this could work with animation, but I'm still stuck at the modelling stage for the moment...
By the way, Michael, I followed this workflow because you recommended viewing Andrew Hakim Lee's Ornatrix workflow on another post :-)
Michael, does the hairstyle work on your PC?
Could there be any efficient workaround to have the hair working? I can't wait any longer because of deadlines.
Thank you,
Ryan.
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Edit 1: I opened the scene on other PCs with 3ds Max 2014, Ornatrix 4.03 4140 and VRay 3.20.02. it does not work either (producing the same result as showed on my first post).
Also, if this works on your pc, please could you upload the working scene?
Edit 2: this does not work on 3ds Max 2013, Ornatrix 4.03 4140 and Vray 2.40.
Note that I applied the same creation pipeline on 2 other hairstyle and it didn't work either (on clean 3ds max instances). Could it be a modifier stack bug when using multiple "edit guides" along with "ox hair from guides" ?
I didn't check with previous Ornatrix version as I don't own older versions.
Edit 3: Here are the differencies between Vray RT and Vray in production mode, using VRay 3.20.02:
