Solved by ptrblck in post #2 
              
              
                nn.LSTM expects the a tuple with the hidden_state and cell_state as the second argument, so this code should work: 
x, hidden = self.lstm(actions, (torch.zeros(1, 2, 128), torch.zeros(1, 2, 128)))

Unrelated to this problem, but note that you are reassigning x and this the output of self.input_fc wi…