I have just spent an hour debugging my first progress code for clone_from.

I had a silly bug in my code, but because of this:

       try:            handler(line)        except Exception:

I did not see any errors.

This code is in _dispatch_single_line or func handle_process_output in cmd.py

I do not see why you have this try handler at all.
Given that I have no logger file setup in my code that this experiment was conducted in
the logged error is silent.

I recommend that you remove the try/except altogether.

If you have a good reason to keep the try/except then use
log.exception( 'msg' )
that will include the traceback details.