Solved by harsha_g in post #6 
              
              
                Why call each time? Just once will suffice à la 
criterion1 = nn.CrossEntropyLoss(weights_label_0)
criterion2 = nn.CrossEntropyLoss(weights_label_1)
criterion3 = nn.CrossEntropyLoss(weights_label_2)

loss_1 = criterion1(output[0], label_0)
loss_2 = criterion2(output[1], label_1)
loss_3 = criterion3(…