Looking at the stack trace this is a similar issue as the "no_proxy" one, but in some sense worse because it happens when just calling a regular unix API (not an Apple framework API).

The first few lines of the stack trace are for code in the "Network" framework which is new in macOS 10.14 and is based on lib dispatch and  hence uses threads. That results in the same problem as the "no_proxy" one: code that causes problems when called after os.fork().

That's a bug in macOS.

In Python 3.8 the multiprocessing module switched to "spawn" mode instead of "fork" mode because of this.  You can do this manually for earlier versions (https://docs.python.org/3.7/library/multiprocessing.html#contexts-and-start-methods)

P.S. A reproducer would still be nice as that would make it easier to raise and issue with Apple about this.