Hi,
as Marco Hess pointed out in kicad developers mailing list, if DXF R12 is used e.g. through LibreCAD, ellipse are converted to line segments and then kicad will load it correctly.
if the ellipse will be not completely closed it is easy to add a small segment to the pcb edge and the board will render fine also in 3d-viewer…
thanks Marco!
PS Marco has patched also the “missing closing ellipse” 
Regards
Maurice