cupy.cuda.cudnn.CuDNNError in NStepLSTM · Issue #1803 · pfnet/chainer

I'm trying to use NStepLSTM like as follows. But if n_layer is more than 2 (n_layer>=2), I get error 'CUDNN_STATUS_BAD_PARAM'. When n_layer==1, my code make success. Is there anything wrong in my c...