Looks like used grass patches are too big for such surface and even facing to terrain normal and scaling them accordingly doesn't fix such look.
Using smaller clumps on problematic areas should fix it. I would suggest you to activate the Slope Range limit for that Forest object and make a copy of it. Within this second Forest object use smaller patches / detailed preset to cover the rest of the Slope Range. Attaching screenshots showing such work-flow. Hope you'll find it useful.