LSTM预测模型：损失值不会改变

I'm trying to implement a simple LSTM prediction model in keras for timeseries. I have 10 timeseries with a lookback_window=28 and number of features is 1. I need to predict the next value (timesteps=28, n_features=1). Here is my model and the way I tried to train it: I'm trying to implement a simple LSTM predictio