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I had the same issue using navigation controller and push other controllers to it. I tried to use Buffered Navigation Controller and several other approaches, but it didn't work for me. After spending some time for figuring it out I noticed that this issue occurs if you trying to push new view controller while previous transaction (animation) in progress (about 0.5 sec duration I guess). Anyway, I made quick solution with delegating navigation controller and waiting for previous animation finishes.
'Unbalanced calls to begin/end appearance transitions for '
Says an animation is started before the last related animation isn't done. So, are you popping any view controller before pushing the new one ? Or may be popping to root ? if yes try doing so without animation i.e. [self.navigationController popToRootViewControllerAnimated:NO];
And see if this resolves the issue, In my case this did the trick.