Unfortunately I don't have an iPad to test on, so I was notified by Apple's review team about the issue. I'm not sure what model they use but here's a screenshot http://a915.phobos.apple.com/us/r30/Purple122/v4/39/39/09/39390931-076b-8e8f-5178-45064e7d 00d5/temp..eoaywlij.PNG
I looked through the list of icon dimensions in that link and the only two I could possibly have that I don't are 167x167 and 87x87, both of which are marked as optional. The 167x167 is labeled 'Home screen on iPad Pro' so it's possible that Apple uses iPad Pros for their reviews, and that's why the icon is missing for them. I don't know why it would be marked as optional if that's the case, but it seems like the only explanation.
After searching around for a more updated icon/splash screen generator I've found https://github.com/eberlitz/splashicon-generator which seems to generate those extra icons I need. I'll try adding those new icons, submit the app, and hope that it works.
So technically Apple's not complaining because an icon is missing, but because the icon on the iPad Pro is obviously disparate from your other icons. Because Cordova supplies this icon as a default, you must override it. It's "optional" because if the icon itself were missing, the OS could infer it from other sizes (but this may not result in the best quality), but it's not optional here because there is an icon there -- it just doesn't line up with your other icons.
Side note: I'm not sure if you're using the CLI or PGB, but if you're using the CLI, you might want to consider using launch storyboard images so that you can get native resolution on the iPad Pro 12.9". As it stands right now your app will be scaled up on a 12.9" iPad Pro.
One last thing: Xyfir-Books-PhoneGap/app.js at master · Xyfir/Xyfir-Books-PhoneGap · GitHub may be a problem. Apple often rejects apps that are wrappers for websites. You should instead bring as much code as possible local to the device and use XHR/AJAX to communicate with your backend.
> So technically Apple's not complaining because an icon is missing ...
That makes a lot of sense.
> I'm not sure if you're using the CLI or PGB ...
I'm using PhoneGap Build. I've since created a new higher resolution screen for iPad Pro, so it shouldn't have to scale up.
> One last thing ...
Yes, I've heard this before, however as of yet I haven't had any issues (I've published 3 other apps before this one started giving me troubles). Probably they just missed it, but should they catch it I can definitely fix it. Until then I'll wait.
Thanks to both of you, I think this should solve my issue, I'll upload a new build tomorrow and hope it gets accepted.