Every now and then this happens on a small or sometimes pretty big scale.
What is causing it and how do I fix or prevent this from happening?

I'm having exactly the same issue. On the editor seems fine but in the game is bugged.

Hey Guys, still here in 2020 and got the same problem. Any fix available?




Edit: Could have something to to with that sand texture. As I changed the texture of the terrain to that grassy dirt texture, and painted sand at places where I wanted beaches to be, no problems any more. Hope this helps someone :)