Well it shouldn’t but it all depends on a multitude of things. It can be caused simply by having weak hardware, most likely GPU but as you say you have the recommended specs that shouldn’t be it.
It can also be happening because the grass is too thick and the view distance is too far. No need to render grass that doesn’t take up more than a few pixels on screen and perhaps you could lower density and still have it look good?
It’s also highly dependent on the grass itself. How many vertexes or triangles does it have? Does it use LODs? (Simpler versions of the same mesh that are shown the further away you get) and how big part of the actual model is transparent?
Rendering tons of transparency is very costly for performance but having less dense grass, LODs and minimizing the transparent parts of the mesh all helps with that.
Another very important thing is how the grass are placed in the level? Did you place them by hand? Were they placed by the Foliage tool or Procedural Foliage or perhaps the grass function in landscape material? The first of these is bad and will cost much more than the others since it won’t instance the grass which saves performance. I would recommend using the grass tools: https://docs.unrealengine.com/latest/INT/Engine/OpenWorldTools/Grass/QuickStart/index.html
It can also be caused by the shader but I wouldn’t say it’s likely in this case.
One other thing that will help tons but might not be desirable is to turn off shadows for the grass.
Hope that helps. You’ll find examples all over the forum, answer hub and the wiki on how to do all this.