Azz131: Thanks for the screenshots. However, the DXF file would be more helpful for testing and helping you with the problem.
If I understand the problem correctly, only the spline at the right is rendered incorrectly by Sketchup. One simple solution would be to explode the splines in QCAD (Modify > Explode), then save again. This will convert the splines into polylines which are generally better understood by applications reading DXF files.