Issue using lr_find() with TextList.from_csv()

For text classifier, I am loading the data from a CSV file post-training language model.

data = (TextList.from_csv('/content/models/processed', 'cleanedData.csv','text', vocab=data_lm.vocab)
               .databunch(bs = bs))

It creates the desired data bunch but when I try to do lr_find() I get #na# in my valid_loss. Whereas using the same command with same file for language modelling works. The only thing different is vocab and label_from_df.

learn = text_classifier_learner(data, AWD_LSTM, drop_mult=0.5)

I have tried giving start and end range for lr_find() but still no result.