Is it a Problem if Training Data and Evaluation Data are Very Similar?
In general, in Machine Learning, if the train set and test set are very similar, then it leads to a small ability to generalization. In other words, the model not performing well on new data. It's called overfitting.

In your case, could be happened more, if some rows are the same in train and data set, then we could say that it's data leakage.