Sometimes this happen if your model is overfitting. you have to make sure that you're not overfitting that much. You should try different approach or different algorithm you will see the result will change most probabily

Exactly, I just made a submission that received a better public score but my old score is what is being displayed on the leaderboard. Kindly fix this Zindi. Thanks.

I think this is because the model is badly overfitting?. you got the better score in private leaderboard but the public score is still the old one.