Dforce hair not showing up in render. [Solved]
Hi! I actually solved this problem on my own but only after thoroughly searching the forums and not finding a solution. I decided I should leave a post so other people in my situation might find it.
I was using MRL DForce Mid-length hair and had this strange problem. Suddenly 85% of the hair was gone in both the viewport and render.
After reloading about 20 times and swapping out the hair a couple more times I figured out what was going on. I had the model's Sub-D set to 4 and that was messing the hair up. Bringing it down to 3 fixed the problem. Most of the simular threads I found on the forum mention the geometry editor being the selected was the issue. For me, the problem did arise after using the weight map editor on a completely different object, so maybe that had something to do with it, but I doubt it.
So yeah. High Sub-D may be what's messing up your hair.