Another thing I noticed:
if I try to include the subtrees in the training (that is, modifying the following line, while leaving everything else unchanged):
train, val, test = torchtext.datasets.SST.splits(
    TEXT, LABEL, train_subtrees=True, fine_grained=True)

I get the following:
ValueError: Expected input batch_size (10) to match target batch_size (2).
So I don’t know if the error is due to something peculiar to the SST dataset or torchtext, but I just couldn’t wrap my head around it… So please, if anyone encountered something similar, what could be the root of the problem?