Hi Caruso,
the shape of x is [162, 1, 64, 64]  and the shape of y is [162, 1] before I input them to the model. The shape of the model output y_pred is [162, 1]. I only use MSELoss for my loss in the training and testing loop.
The warning doesn’t appear when I use 1568 as input  for the flatten layer. I just don’t understand why.