ViewController.m

//
//  ViewController.m
//  cvtest
//
//  Created by Paul Wilkinson on 10/2/17.
//  Copyright © 2017 Paul Wilkinson. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController {
    UICollectionView *_collection;
    NSArray *_values;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
    _collection = [[UICollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:layout];
    _collection.dataSource = self;
    _values = @[[UIColor redColor], [UIColor greenColor]];
    [_collection registerClass:[UICollectionViewCell class]
    forCellWithReuseIdentifier:@"reuse"];
    [self.view addSubview:_collection];
    _collection.frame = self.view.bounds;
    
    double delayInSeconds = 2.0;
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
        [self triggerBatchUpdate];
    });
}

- (void)triggerBatchUpdate {
    [_collection performBatchUpdates:^{
        _values = @[[UIColor blueColor], [UIColor yellowColor], [UIColor redColor]];
        [_collection moveItemAtIndexPath:[self index:0] toIndexPath:[self index:2]];
        [_collection insertItemsAtIndexPaths:@[[self index:0]]];

        
        // Works with this line
        //    [_collection moveItemAtIndexPath:[self index:1] toIndexPath:[self index:1]];
        
        // Fails with this line
        //[_collection reloadItemsAtIndexPaths:@[[self index:1]]];
    } completion:^(BOOL finished) {
        [_collection reloadItemsAtIndexPaths:@[[self index:1]]];
    }];
}

- (NSIndexPath *)index:(NSUInteger)ind {
    return [NSIndexPath indexPathForRow:ind inSection:0];
}

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

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView
                  cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    UICollectionViewCell *cell = [_collection dequeueReusableCellWithReuseIdentifier:@"reuse"
                                                                        forIndexPath:indexPath];
    cell.backgroundColor = _values[indexPath.item];
    
    return cell;
}


@end