I know this is old but I found this post when I was looking for a solution to this and was disappointed to see no response. This is a problem with changing the WindSpeed input in SimpleGrassWind - it will jitter the vertices. Don’t think there’s any way around it, unfortunately. Fortunately, you can kinda get a similar effect by modifying the WindIntensity. There’s a good video on setting this up (for grass and trees) here: Simple Global Wind in UE4 (One weird trick! Everyone hates him!) - YouTube