Now you can see what you can also see in the first pictures if you look very closely. There are closely spaced vertices which, roughly speaking, look like a corner.
It is a very special triangulation that your software provides. I can see the division into 4 instead of the usual 2 triangles in the frame. You can do something like this, see Rounded corners on BoxGeometry where faces not touching - #4 by hofk
Do you have to process exactly this existing data and get the identical wireframe?