Different results for LogisticRegression on python 2.7 and 3
Assuming that you are using sklearn, if you go to the source in the github 
you will see that they do not differ. 

But you have variability elsewhere. For example train_test_split of sklearn also takes random seed, so it could be that your data is fundamentally different between these approaches (you could do cross valdiation for example to include all the data in train and test)