Can be reproduced with the multiprocessing demo.

Current workaround is to always force "spawn":

multiprocessing.set_start_method("spawn")

However, needing to do this will definitely bite Linux users since "fork" is the default.

See: https://docs.python.org/3/library/multiprocessing.html#contexts-and-start-methods