The models for curve fitting in my lab were using lambdas, which cannot be serialized by multiprocessing/pickle (at least that was the state about 5 years ago). The pathos.multiprocessing module [1] served as a drop-in replacement, which was able to handle lambda with its own dill serializer. Saved me quite a bit of refactoring.
[1] https://github.com/uqfoundation/pathos