No loss ids in truncated sequence (GPT2 model)

[ngavcc]

I am using GPT2 model + MixedTemplate for a text classification task
When i am training, an exception occur at reshape tensor operation
I have made some inspection and i realized that when input text is too long, it turn out that all value in loss_ids is zero, and model failed to train (exception at reshape tensor when model getting output for "mask" position)
This is an example of batch data (from PromptDataLoader), when i use batch size = 2048, i got loss_ids of shape torch.Size([2048, 128]), but when i sum it's elements value (loss_ids.sum()), i only get tensor(2047). that means one data instance get no loss_ids