title: tensorflow warning - Found untraced functions such as lstm_cell_6_layer_call_and_return_conditional_losses
body: <p>I'm using tensorflow2.4, and new to tensorflow</p>
  <p>Here's the code</p>
  <pre><code>model = Sequential()
  model.add(LSTM(32, input_shape=(X_train.shape[1:])))
  model.add(Dropout(0.2))
  model.add(Dense(1, activation='linear'))
  
  model.compile(optimizer='rmsprop', loss='mean_absolute_error', metrics='mae')
  model.summary()
  
  save_weights_at = 'basic_lstm_model'
  save_best = ModelCheckpoint(save_weights_at, monitor='val_loss', verbose=0,
                          save_best_only=True, save_weights_only=False, mode='min',
                          period=1)
  history = model.fit(x=X_train, y=y_train, batch_size=16, epochs=20,
           verbose=1, callbacks=[save_best], validation_data=(X_val, y_val),
           shuffle=True)
  </code></pre>
  <p>And in some epochs, got this warning:
  <a href="https://i.stack.imgur.com/cWBlr.png" rel="noreferrer"><img src="https://i.stack.imgur.com/cWBlr.png" alt="enter image description here" /></a></p>
  <p>Do you know why did I get this warning?</p>