I have a few bugs to report, and this appears to be the closest thing to where I would do that.
First, the "skip to next" button, iOS 9.2, iPhone 6 plus. Crashes every time.
Second, if I download a lesson, and listen to it streamed, it doesn't put the media player controls on both pages, even though they're the same page, same lesson. I'm going to guess it's a navigation controller that pushes a the same VC either way, so whoever coded your model missed something.
I believe the "skip to next" crash happens also on the lock screen, as it just stopped when I hit the "next" button. I know you guys just hired an iOS programmer last year, so tell him/her to get these things going. I make too much here to justify coding in Japan, but if I can make my own app and get it going, then the revenue won't be an issue and I can go fix those bugs, hehe.
Let me know if there's a better platform for bug-reporting, or if you don't have an iOS programmer and want these fixed. If they used HTML5 or Xamarin, well... the app responds too well to be HTML, uncertain about the other one, just C# though.
Later (I did weatherCaster's UI and SmartGlass UI, familiar with iPhone quite)
Marking something complete without network connection blocks UI until the server can communicate. I wouldn't do this. Instead, store it locally and wait for a network connection.
If it's under a total of 3MB (I think the limit is 5 now) use NSUserDefaults, otherwise archive an NSMutableDictionary into the library folder. (I think, library or cache is emptied every start, documents if not library). They'll need to use NSKeyedArchiver, it's annoying but the best way to bypass the iCloud limitations that user defaults will impose (It auto-syncs, which is why I don't recommend using NSUserDefaults, even though it's in every manual)
Edit: Add that if the player/controls are showing on a lesson, then the table view doesn't increase the scrollRect content area and you can no longer click on the last couple items, as they do not go above the player.
Beginning to think the coder isn't the issue, so much as testers being necessary