Launch Multiple generations

The problem is that the Unity Terrain Engine (UTE) does not work in absolute heights.
UTE uses a relative height value (0-1) multiplied by a factor.
In addition, UTE stores the values in the filesystem as ushort, which gives an actual range of 65,536 values.

By default, to efficiently use this range and increase vertical accuracy, RWT finds the maximum and minimum altitude values in the generated area, and convert them in UTE elevation range.
Each terrains generated in separate runs has its own unique maximum and minimum height, which gives the effect as in your screenshot.

To work around this, use a fixed elevation range:

prefs.elevationRange= RealWorldTerrainElevationRange.fixed;
prefs.fixedMinElevation= -1000;
prefs.fixedMaxElevation= 9000;