- The outer limits, in layer US-SITE-RWAY, are not always closed. Isolate layer, try PEDIT - Multiple, <select all>, Join. You will see, not all the resulting polylines are closed. Fix them and then you can use the resulting polylines or you can explode them.
- After that, extend both ends of the US-SITE-LAND-PROP lines a few units, to be sure they intersect the border. In your sample, a lot of them are not exactly on the border, sometime missed by just 0.0002 units.
- Use overkill, ignoring layer, color, linetype etc.
- Process one island at the time.
Use the attached lisp.
You will still get some errors, especially in the curved islands... The tangent lines and arcs are not connected, not tangent, or fails for no particular reason, even for some Autocad native commands.