Tried on default model, same happens. Investigated on other ddaamm hairs scalps, most have this same look, others have the holes on the side of the head.
Looking elsewhere I found the culprit, it's Hunting Succubus Automatic Body Smoother on the session plugins. It has an option to disable tesselation on the back of the head, which still does some holes on the top.
I wonder if I can get by without it, I use Skin Micro Detail from northern.shikima too.
It seens having any of those active causes the issue.