Could you print the shape of x just before the .view call?
I think 3200 is the wrong number here and thus your batch size will increase.
You are pushing “everything left” into the batch dimension using view(-1, 3200). So if x has 6400 features, the batch dimension will be doubled.
You could use x = x.view(x.size(0), -1) instead, which will give you a size mismatch error in the next linear layer.