I've found the bug and submitted the fix for the missing characters in our iOS 8 update version, 2.6.0. It turns out that the problem only shows up on 32-bit devices. Apple broke a text sizing function on 32-bit devices, so text in several places throughout the app was being rendered with a font size of 0. Most significantly, reading, definition, and tone prompts don't show the prompts, and the word detail screen doesn't show the word.
I am not sure how long it will take to get the app update approved, but hopefully they can expedite it. In the meantime, you may still be able to do some study if you use Advanced Study and only do writing prompts, or if you'd like to try the HTML 5 version on your iOS device, or if you want to do the Flash version on your computer.
I'm sorry about this, guys. It's my fault; I should have tested on more devices for this update. Thanks for your patience.