How to fix error 'argument 1 must be an iterator' using label_delim in fastai?

I'm trying to follow an tutorial of classifying images on the Planet Amazon dataset here (also described in fastai's documentation), but I'm having problems using the function label_from_df(label_delim=' '), resulting in the error TypeError: argument 1 must be an iterator.

Searching for a solution, I saw this question on SO, but the csv file handling is being done on fastai, so I don't believe it fits here.

The context of the code is the following:

src = (ImageList.from_csv(path, 'data.csv', folder='images', suffix='.jpg')
       .split_by_rand_pct()
       .label_from_df(label_delim=' ')
      )

If more lines of code are needed to understand the problem, it can be provided.

I'm using my own dataset for training on Google Colab, and I don't believe there is a problem in the csv file or the images folder, though it is a possibility.

The error when running the mentioned line is:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-18-69a35763cde8> in <module>()
      2 src = (ImageList.from_csv(path, 'data.csv', folder='images', suffix='.jpg')
      3        .split_by_rand_pct()
----> 4        .label_from_df(label_delim=' ')
      5       )

3 frames
/usr/local/lib/python3.6/dist-packages/fastai/data_block.py in _inner(*args, **kwargs)
    473             assert isinstance(self.train, LabelList)
    474             kwargs['label_cls'] = self.train.y.__class__
--> 475             self.valid = fv(*args, from_item_lists=True, **kwargs)
    476             self.__class__ = LabelLists
    477             self.process()

/usr/local/lib/python3.6/dist-packages/fastai/data_block.py in label_from_df(self, cols, label_cls, **kwargs)
    281             new_kwargs,label_cls = dict(one_hot=True, classes= cols),MultiCategoryList
    282             kwargs = {**new_kwargs, **kwargs}
--> 283         return self._label_from_list(_maybe_squeeze(labels), label_cls=label_cls, **kwargs)
    284 
    285     def label_const(self, const:Any=0, label_cls:Callable=None, **kwargs)->'LabelList':

/usr/local/lib/python3.6/dist-packages/fastai/data_block.py in _label_from_list(self, labels, label_cls, from_item_lists, **kwargs)
    270         labels = array(labels, dtype=object)
    271         label_cls = self.get_label_cls(labels, label_cls=label_cls, **kwargs)
--> 272         y = label_cls(labels, path=self.path, **kwargs)
    273         res = self._label_list(x=self, y=y)
    274         return res

/usr/local/lib/python3.6/dist-packages/fastai/data_block.py in __init__(self, items, classes, label_delim, one_hot, **kwargs)
    407     _processor=MultiCategoryProcessor
    408     def __init__(self, items:Iterator, classes:Collection=None, label_delim:str=None, one_hot:bool=False, **kwargs):
--> 409         if label_delim is not None: items = array(csv.reader(items.astype(str), delimiter=label_delim))
    410         super().__init__(items, classes=classes, **kwargs)
    411         if one_hot:

TypeError: argument 1 must be an iterator