The way parallelism is implemented requires pickling (using dill) to transfer information between processes. Some change between versions 0.3.4 and 0.3.5 of dill broke things in a couple of ways. Options objects from optionsfactory stopped being picklable - this is now fixed in the latest version (see johnomotani/optionsfactory#16), but pickling of TokamakEquilibrium objects is still failing - see uqfoundation/dill#510.