Unexpected corpora loaded

after a certain amount of steps (always about 15k) the message “weighted corpora loaded…” appears between the normal messages of information about the steps. Then after few more steps there is the following error:

File “/home/bavaroff/anaconda3/envs/openNMT/lib/python3.7/site-packages/onmt/inputters/dynamic_iterator.py”, line 231, in _bucketing
for ex in self.mixer:
RuntimeError: generator raised StopIteration

Any solution?