The rules have changed a bit for those who haven't observed

Note that there are Public and Private Leaderboards. The Public Leaderboard excludes approximately 50% of the test dataset. While the competition is open, the Public Leaderboard will rank the submitted solutions by the accuracy score they achieve. Upon close of the competition, the Private Leaderboard, which covers the other 50% of the test dataset, will be made public and will constitute the final ranking for the competition.

Whether I am a victim of leaderboard overfitting or not, I am happy Zindi took this great initiative. This will help us trust our validation scores more, and become better data scientists !!!!