UICollectionView Assertion failure in -[UICollectionView _updateWithItems:tentativelyForReordering:]
I found this rdar: http://www.openradar.me/26280932 which says:
Calling insertItemsAtIndexPaths: on UICollectionView after viewDidLoad but before viewDidAppear: will cause an assertion failure in -[UICollectionView _endItemAnimationsWithInvalidationContext:tentativelyForReordering:]. Calling reloadData in the same scenario doesn't generate the assertion.
So you could check if you are doing your call before viewDidAppear and adjust/wait before view did appear.