I am suspecting that the pickle.load (or now torch.load if you changed to use that) are not playing well with multiprocessing somehow. Could you comment that out, and put something like feature=None and see if you can iterate through the dataset?
If you don’t mind, could you try installing pytorch from the github source? There have been a number of improvements on dataloaders since last release. Some of them are specifically done to prevent dataloader from hanging. The instructions in README.md 13 at https://github.com/pytorch/pytorch 26 are not very complicated.