@wielkiczarnyafgan: Thx for the tipp. I’ve checked the settings on the landscape but they are the same as in the demo scene. Max LODLevel: -1, Export LOD = 0. LODDIstacneFactor = 1 and LDFalloff = Linear. Any other idea what could cause that weird behavior ? 
UPDATE: I’ve checked also the demo scene and it seems like there’s the same behavior on the grass material only. The rock and dirt material (Layer 2 and 3) behave correctly, only when I paint the grass material the ground starts “moving”. Can anyone reproduce this effect ? Oh and it seems that in my own scene, rock and dirt material “wobble” too
Also I wanted to ask you how I can adjust the water speed on slopes ? IMO I think it’s too fast in the demo scene.