I have a UICollectionView that while scroll in occasions stops updating cells. It load a few cells but when I scroll down or up the rest of the UIcollectionView is empty although the contensize is bigger that the few cells visibles sizes.

It happens more when I scroll really fast, randomly cellForItemAtIndexPath stops being called and the UICollectionView only shows the last loaded cells, with the rest of the space empty.

Here is my code:

[self.collectionView registerNib:[UINib nibWithNibName:NSStringFromClass([NewsCollectionViewCell class]) bundle:nil] forCellWithReuseIdentifier:NSStringFromClass([NewsCollectionViewCell class])];

[self.collectionView registerClass:[NewsHeaderCollectionReusableView class]  forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:NSStringFromClass([NewsHeaderCollectionReusableView class])];

pragma mark UICollectionViewDataSource

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
return 1;
}

- (NSInteger)collectionView:(UICollectionView *)collectionView
 numberOfItemsInSection:(NSInteger)section
{
return self.newsArray.count;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView
              cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
NewsCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:NSStringFromClass([NewsCollectionViewCell class]) forIndexPath:indexPath];

[cell refreshWithContentModel:self.newsArray[indexPath.item]];

return cell;
}

- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView
       viewForSupplementaryElementOfKind:(NSString *)kind
                             atIndexPath:(NSIndexPath *)indexPath
{
NewsHeaderCollectionReusableView *collectionReusableView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:NSStringFromClass([NewsHeaderCollectionReusableView class]) forIndexPath:indexPath];

if (self.newsArray.count) {
    [collectionReusableView refreshWithContentModel:self.newsArray[0]];
}

return collectionReusableView;
}

pragma mark UICollectionViewDelegate

- (void)collectionView:(UICollectionView *)collectionView willDisplayCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath
{
if (indexPath.item == self.newsArray.count - 1) {
    [self addMoreNews]; // add items to array and call collection reloaddata
}
}

pragma mark UICollectionViewDelegateFlowLayout

- (CGSize)collectionView:(UICollectionView *)collectionView
              layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{    
return CGSizeMake(ceilf(self.collectionView.bounds.size.width / 3.0) - 10, ceilf(self.collectionView.bounds.size.height / 3.0));
}

- (CGSize)collectionView:(UICollectionView *)collectionView
              layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section
{

return CGSizeMake(self.collectionView.bounds.size.width, ceilf(self.collectionView.bounds.size.height / 2.0));
}