Many thanks for the reply !
I cross-checked the generated batches using consecutive calls of next(iter(dl)). The batches are different.
So the base_seed generated by the main process is different than the seed fixed manually using torch.manual_seed? Also, if I interpret it, for each epoch, the workers will be assigned a new seed base_seed + worker_id. And the data augmentations will be based on the new worker seed?