about crf result

hi:
 Thanks for sharing! but when i use crf layer of your model,
crf = CRFLayer()
pred = crf([pred, sequence_lengths])
the printed f-score are all 0,and early stop occured.
but when use the origin model(that is no crf) the result is sometimes ok,
can you give some suggestion on how to make crf layer better?thanks 