To all artists using Daz studio for renders, if you want to avoid the "black lines" on foreheads: 1) Select the hair 2) Then switch to the the "Geometry editor tool" 3) Go to the "Tool Settings" tab and "hide" the "Cap" (Click the eye icon next to "Cap")
This will remove the hair cap's geometry from the render and prevent the "black lines" but not remove it from the actual scene so no need to worry about hair going wonky because cap is gone.