This happens to me as well. For some reason, it decides to use the main menu camera animation on the loot box items – panning slowly from left to right. I did find if I click where the loot item would normally be it opens the preview like normal so I can see what I got. I found out I got the Masquerade Reaper skin from doing this.
Oddly, the Huitzilopochtli Zenyatta skin from the main menu is still visible after the animation pans all the way to the right. My guess is that the camera animation is tied to the models, and since Zenyatta isn’t being deleted when opening a loot box, the camera jumps back to its previous animation.