@ everyone with a Radeon card:
Try editing your serverconfig.xml section World.
Insert your World size and Seed like this (replace it with your wishes)
<property name="GameWorld" value="RWG"/>
<property name="WorldGenSize" value="10240"/>
<property name="GameName" value="JamesKirk"/>
<property name="GameMode" value="GameModeSurvival"/>
Then start 'startdedicated.bat'
Don't worry, it takes really long (this seed&size 50min on an i7-8700k/16GB with Radeon RX480/8GB) !
I got a playable world with smooth surface and no tall ridges (like a combed landscape).
Stop the server, and restart a normal game.
That's it
Yesterday I wondered why it took only 5:28min to generate a 8k map. With every 2nd row missing, it was only half the time ;-)