I had a similiar issue with V4, the lashes came out looking sparse and "jagged" looking and I someone replied with [I have written down in my trusty book...because I can't remember squat]
Using a Min shade rate of .2 then set pixel sample to 5, then change max texture size to 1k-4k and after changing make sure to check reload textures if you have keep textures loaded turned on.

It does make your rendering go a little slower but it does "fill in the blanks" on the lashes.

If that doesn't help, it might be too your map for the lashes? Try some merchant resources to bulk up your lashes, by blending several together?