This problem does not appear to be a race condition ("Time Of Check To Time Of Use" bug) in my case as the directory in question exists both before and after the os.listdir call.

I got a workaround saying to wrap the os.listdir call in try/except in my Stack Overflow question at https://stackoverflow.com/questions/55067904/python-os-listdir-fails-with-filenotfounderror-when-directory-exists.  This worked as no longer got any spurious FileNotFound exceptions.

I realize that the code snippet I gave is not runnable.  I'll look to put together a small example illustrating the problem and add to the issue.