OK - I get it now, messing a bit more I see this is an IGES import - I believe this is this bug, at least partly:
RH-3894 All one edge
I will see if I can bump this bug- it rears its head from time and it is a pain to deal with…
See if this helps for now - RetrimSrf.py (2.6 KB)
To use the Python script use RunPythonScript, or a macro:
_-RunPythonScript "Full path to py file inside double-quotes"
-Pascal