The error doesn’t seem to be related to DDP, but the DataLoader and torchtext:
TypeError: default_collate: batch must contain tensors, numpy arrays, numbers, dicts or lists; found <class ‘torchtext.data.example.Example’>

I’m unsure how the torchtext.data.example.Example class is implemented, but could you try to return tensors in the Dataset.__getitem__ instead of this object?