I’ve finally had time. I see the mitered corners you were talking about. I also see that every straight line is divided into many segments which doesn’t make sense. There are 22 segments in that “straight” line. There’s 999 segments in the whole outline.
I expect you are running into a situation where the segments at those corners are so short, SketchUp is doing a bit of approximating. I think sort out why the DWG file ends up with all those short line segments and correcting it will go a long way to fixing this problem.
I’m curious though why you wouldn’t just draw that in SketchUp in the first place. It’s a pretty simple shape and I think it would be easier to just start in SketchUp.