The error does not always happen 100% of the time, but the frequency is high, maybe 80%.
Main Terrainbuilder.exe does not freeze, just the scene.
I've imported 70 .shp files for a total of 258mb into my current map scene.
MainThread=3988 is not always the same size when trying to import. It varies but still produces the same error when importing the same .shp file.