Edit3: I found a small bug. In some instances the corners of terrains do not align properly. I noticed there is a WeldCorners method that is called when the terrains LOD switches, however there are some instances where Draft terrain are not used at all; in these situations WeldCorners is not called. As a result, sometimes the corner x value and corner z value stored in a terrains Edges container do not match, even though they should represent the same value. When the Edges are written to the terrain, the z values are written last so corner z value becomes the final value of the corner; as such, terrains align properly with their left/right neighbors but not their top/bottom neighbors at the corners.
upload_2020-6-12_19-9-53.png
This was tested in the tutorial scene with Drafts disabled.