After 2 months of updates, I finally got this app store rejection in my last version update:
Legal - 5.1.1
We noticed that your app requires users to register with personal information prior to accessing non account-based features, which does not comply with the App Store Review Guidelines. Specifically, It would be appropriate to make registry optional at launch for services that are publicly accessible on the website.
Why is this happening to me, when Instagram, LinkedIn, Pinterest, etc all require users to login first before viewing publicly accessible content (accessible from web browsers)? Is there special treatments for huge billion dollar apps now in App Store? I had no problem with Android play store..