keras confusion matrix doesn't match

https://s00hyun.github.io/ml&dl/keras-confusion-matrix-doesn't-match/

shuffle=False

valid_datagen = ImageDataGenerator(rescale=1.0 / 255)

validation_generator = valid_datagen.flow_from_directory(
    validation_dir,
    target_size=(height, width),
    batch_size=batch_size,
    class_mode="categorical",
    shuffle=False,  # For evaluation
)

call reset() in ImageDataGenerator

validation_generator.reset()
Y_pred = model.predict_generator(validation_generator, STEP_SIZE_VALID+1)#validation_generator.n // validation_generator.batch_size+1)
classes = validation_generator.classes[validation_generator.index_array]
y_pred = np.argmax(Y_pred, axis=-1)  # Returns maximum indices in each row