Solved by piapple in post #3 
              
              
                Thank you, Thomas. I realize I made a silly mistake on the optimizer that does not set the learning rate for time_factors: 
    self.optimizer = torch.optim.SGD([
        {"params": self.model.user_factors.weight},
        {"params": self.model.item_factors.weight},
        {"params": self.model.use…