It seems after epoch 25 the model is narrowing down on perfecting the prediction of the training data. The overfitting of the model is after that disregarding any more higher level semantics learned during the first 25 epochs and exchanging it for in detail being able to predict your specific training data, validation is not examples from your training data right?. The generalisation seems to be lost due to too small training data corpus.
I have no clue what happened there after ~125 epochs - did you change training data?