Just found out the problem. It was mainly stupidity of mine: All the RankingCell images were actually .jpg, but named as RankingCell.png.
The reason why this was only occurring in the iPad Mini is because the older images were being loaded from cache on the other devices I tested, for I had ran the app on them before. Unlike the iPad, which had a fresh install. I could reproduce the glitch removing the app from my iPhone and then building it again.
Didn't even know this was possible. And since I was seeing the images thumbnails alright, I never suspected of such thing.