UIPageViewController transition not working correctly - ios

Question

I have a UIPageViewController with a page curl (not that the transition type matters as neither works), where the second page doesn't display until the animation is finished. The code use to work, but no longer, any ideas would be great
The code is as follows:
- (void)viewDidLoad
{
self.pageViewController = [self.storyboard instantiateViewControllerWithIdentifier:#"PageViewController"];
self.pageViewController.dataSource = self;
self.pageViewController.delegate = self;
// other code deleted, for easy reading
}
- (PsalmViewController *)viewControllerAtIndex:(NSUInteger)index
{
if (([self.mDelegate.mPsalms count] == 0) || (index >= [self.mDelegate.mPsalms count]))
return nil;
// Create a new view controller and pass suitable data.
PsalmViewController *controller = [self.storyboard instantiateViewControllerWithIdentifier:#"PsalmViewController"];
PsalmData *data = [self.mDelegate.mPsalms objectAtIndex:index];
[controller setupView:index psalm:data];
self.mNextPsalm = controller;
return controller;
}
#pragma mark - Page View Controller Data Source
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController
{
if (self.mNextIndex == 0 || self.mNextIndex == NSNotFound)
return nil;
self.mNextIndex = self.mPageIndex - 1;
self.mAnimating = true;
NSLog(#"Prev %lud", (unsigned long)self.mNextIndex);
return [self viewControllerAtIndex:self.mNextIndex];
}
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
{
if (self.mNextIndex == NSNotFound)
return nil;
if (self.mNextIndex + 1 == [self.mDelegate.mPsalms count])
return nil;
self.mNextIndex = self.mPageIndex + 1;
self.mAnimating = true;
NSLog(#"Next %lu", (unsigned long)self.mNextIndex);
return [self viewControllerAtIndex:self.mNextIndex];
}
- (NSInteger)presentationCountForPageViewController:(UIPageViewController *)pageViewController
{
return [self.mDelegate.mPsalms count];
}
- (NSInteger)presentationIndexForPageViewController:(UIPageViewController *)pageViewController
{
return 0;
}
- (void)pageViewController:(UIPageViewController *)pageViewController didFinishAnimating:(BOOL)finished previousViewControllers:(NSArray<UIViewController *> *)previousViewControllers transitionCompleted:(BOOL)completed
{
if (completed)
{
self.mPageIndex = self.mNextIndex;
[self setCurrentPsalm:self.mNextPsalm];
}
else if (finished)
{
self.mNextIndex = self.mPageIndex;
}
if (completed || finished)
self.mAnimating = false;
NSLog(#"C %d F %d", completed, finished);
}
Again any help would be appreciated, I have no idea what is causing this problem.