[2020] How can prevent this "folding"?

Landscaping tools do not work well with the brush size set to "single" - increase it to show a number and it will behave much better.

You will also want to turn the strength down a lot to something like 0.1

Originally posted by koyangi: I tried to repair but it seems to be impossible.
In the first pic it seems to work out ...
https://steamcommunity.com/sharedfiles/filedetails/?id=2177137111
... but in the following pic you see it cant be repaired since one step later it comletely destroys the area.
https://steamcommunity.com/sharedfiles/filedetails/?id=2177137138
And i did not had this ugly phenomen before and in the editor i cant see it.

Your brush size (Pinselgrösse) is still set to "single" (Einzeln). Turn it up just a little bit so it's a number instead. I think 15 is the smallest the game can do. Then it will stop doing what it's doing right now.