DXF is the file format from hell ! it should be killed, including the program , and company responsable for creating it !
Some versions of autocad can't even read all the versions of DXF !
That being said : what you are seeing is the track losing its 'width' . a track in PCB world is a two coordinate pairs ( begin and end ) and a width.
So that nice oblong pad is converted into a stroke with a width. in dxf you get a zero width line with two circles. the radius of the circles is the width .
Use the solidworks connector. it's free brings all into solidworks directly. don;t use that intermediate crap DXf format.