Hello @all 
I have a common issue related to continuing to train a pre-training model in machine translation task.
When I load the pre-training model and the new dataset, I got an error related to mismatch between tensor sizes.
size mismatch for module.decoder.fc.weight: copying a param with shape torch.Size([609, 256]) from checkpoint, the shape in current model is torch.Size([608, 256]).
size mismatch for module.decoder.fc.bias: copying a param with shape torch.Size([609]) from checkpoint, the shape in current model is torch.Size([608]).

I think this issue related to the vocabulary size self.token_embedding = nn.Embedding(vocab_size, d_model),  because, whenever I build data build_vocab using only one dataset during pre-training and fine-tuning, everything works fine.
Any suggestions to overcome this issue?
Kind regards,
Aiman Solyman