Translation outputs sentences with repeated phrases

I am trying to develop a NMT system for en->ru.
RNN, token=word, 1m lines dataset
But I see that sometimes (too often for a random mistake) system outputs sentence with repeated phrase:
What has the election taught us in London ? -> В лондоне нас учили в лондоне ?
(in London taught us in London)
But at the same time “What has the election taught us ?” translates pretty well.
What could it be?


This usually happens on unexpected data, either because the model was not trained long enough or there is not enough training data.

So, I have to try:
Find more data
increase train_steps
maybe increase complexity of NN architecture? Increase number of layers or something…