I've had the same black render phenomenon a few times, along with random body parts turning black or light purple, and I use CPU rendering which is currently a ryzen 7 on win10. I have a gtx 970 as well but it hasn't rendered anything from Poser since the SM days of P11. It hangs up and does nothing so I have to force close or Poser crashes completely so I just have stuck to cpu rendering ever since cause I can't afford an upgrade and I don't want to stress my ancient card or I'll be out completely lol.

I haven't checked the error messages but if it happens again I will.

Re-rendering randomly fixes the problem, or I'll click a setting on the affected material and that seems to fix it. Sometimes re-importing the image texture has fixed it. Just reloading textures does nothing.