Weird discontinuity lines in my landscape

Hey there,
im fairly new to UE4 and im trying to learn the basics. At the moment i’m trying to fill my landscape with grass, that works perfectly fine. Unfortunatly i’ve noticed some weird lines where no grass is on the landscape but rather goes straight down in an 90 degreee angle under the map. The lines all look like i could have made them on accident but i have absolutly no clue what really happened. I added 2 screenshots for clarification. I hope you can help me :slight_smile: