Invalid update: invalid number of items on UICollectionView

It's a bug with using insertItemsAtIndexPaths on an empty UICollectionView. Just do this:

if (self.birthdays.count == 1) {
    [self.collectionView reloadData];
} else {
    [self.collectionView insertItemsAtIndexPaths:@[[NSIndexPath indexPathForItem:   (self.birthdays.count -1) inSection:0]]];
}

(Can't believe this is still broken in iOS8.)

It is a bug in UICollectionView even in iOS 11, but not exist in UITableView, very easy to reproduce: Assume the following SWIFT code is working:

addItemInDataSource()
collectionView!.insertItems(at: [IndexPath(item: position, section: 0)])

Change it to:

collectionView!.reloadData()    // <-- This new line will make UICollection crash...

addItemInDataSource()
collectionView!.insertItems(at: [IndexPath(item: position, section: 0)])

It will crash...

UICollectionView will lose track of the original number of items in some condition, just add a dummy line before insertItems command will avoid this kind of crash:

collectionView!.reloadData()

collectionView!.numberOfItems(inSection: 0) //<-- This code is no used, but it will let UICollectionView synchronize number of items, so it will not crash in following code.
addItemInDataSource()
collectionView!.insertItems(at: [IndexPath(item: position, section: 0)])

Hope it could help in your situation.