This is also happening to me. Looking into the issue lead me to the issue being related to the bIsMirrored block within the TransformRawMeshVertexData function in MeshMergeHelpers.cpp, but I’m not sure as to the proper fix. The intent appears to be to properly flip the render direction of the surfaces to properly match the transformation. Looking at the difference between 4.17’s section of the same variety, it looks like it would be properly functional and I’m not exactly certain why it was changed.