我的模型定义如下。使用了两个回调函数。我想监控瓦尔_accuracy，并根据损失使用提前停止。

checkpoint_filepath = '/tmp/checkpoint'
model_checkpoint_callback = tf.keras.callbacks.ModelCheckpoint(
    filepath=checkpoint_filepath,
    save_weights_only=True,
    monitor='val_accuracy',
    mode='max',
    save_best_only=True,
    verbose=1)
early_stopping = tf.keras.callbacks.EarlyStopping(monitor='val_loss', patience=1)
history = model.fit(train_ds, epochs=epochs, validation_data=val_ds, callbacks=[early_stopping, model_checkpoint_callback])

为什么它总是抱怨“警告：tensorflow：只能在瓦尔_accuracy可用时保存最佳模型，跳过"？