The circle on the left is showing behaviour that I would expect when exported as a 3d DXF. As the vertices define the edge of the SketchUp segmented circle, when converted into a “true” circle the horizontal edge nevertheless falls short of the boundary in the resulting DXF. If you want the edge to touch the circle boundary then you need to connect the vertices of the circle.
The circle on the right has something strange going on that I think is a tolerance issue. The edge splits the circles’ face and appears to hit a vertex as far as I can see. But in the export the edge does not touch the circle boundary as the edge is actually shorter than the radius of the circle:
My theory is that the vertex of the circle is ever so slightly off the “red axis” that the edge is being drawn along. If I use the rotate tool using a random endpoint of the circle to rotate it back onto the red axis, then redraw the edge, it shows length as 100.000 as expected and exports with the edge touching the boundary of the circle.
In my opinion, it is of no use to have 302 segments in the circle as the “SketchUp circle” will be transformed into a true circle anyway in the export. It also makes inferencing the vertices more difficult as they are closer together/harder to see,48 sides in this case appears to be plenty.