CAAnimation Delegate not called Custom Loading Animation - ios

Question

I'm trying to create a custom loading animation. The animation consists of two parts. First, 5 lines are drawn (animated) outwards. When the lines are finished drawing, they are faded away and the cycle is started over. In order to get this sequential behavior with two animations, I am using two CABasicAnimations, both of which have the same delegate. In the delegate method animationDidStop:, I dispatch to the correct animation (animation 2 if animation 1 just finished, and vise versa). Here is the relevant code:
-(void)startAnimating{//this method launches the line growing animation
self.hidden = NO;
BOOL delegateSet = NO;
animationPhase = 1;
for(CAShapeLayer * pathLayer in _lines){
[pathLayer removeAllAnimations];
pathLayer.strokeColor = _strokeColor.CGColor;
CABasicAnimation *pathAnimation = [CABasicAnimation animationWithKeyPath:#"strokeEnd"];
pathAnimation.duration = .95;
pathAnimation.fromValue = [NSNumber numberWithFloat:0.0f];
pathAnimation.toValue = [NSNumber numberWithFloat:1.0f];
if(!delegateSet){//just set one delegate
pathAnimation.delegate = self;
delegateSet = YES;
}
[pathLayer addAnimation:pathAnimation forKey:#"strokeEnd"];
}
}
//this delegate method dispatches the next animation
- (void) animationDidStop:(CAAnimation *)anim finished:(BOOL)flag{
if(animationPhase == 1)[self fadeLines];
else if(animationPhase == 2)[self startAnimating];
}
-(void)fadeLines{//this method launches the fading animation
self.hidden = NO;
BOOL delegateSet = NO;
animationPhase = 2;
for(CAShapeLayer * pathLayer in _lines){
[pathLayer removeAllAnimations];
CABasicAnimation *strokeAnim = [CABasicAnimation animationWithKeyPath:#"strokeColor"];
strokeAnim.fromValue = (id) pathLayer.strokeColor;
strokeAnim.toValue = (id) [UIColor clearColor].CGColor;
strokeAnim.duration = .2;
if(!delegateSet){//just set one delegate
strokeAnim.delegate = self;
delegateSet = YES;
}
[pathLayer addAnimation:strokeAnim forKey:#"animateStrokeColor"];
pathLayer.strokeColor = [UIColor clearColor].CGColor;
}
}
So this all works great when it's run on it's own (not while other things are being done in the background). But when I use it as a loading animation (while other things are being done in the background), the first initial grow animation is performed, but animationDidStop: is never called.
I've tried using transactions with completion blocks instead of using the delegate pattern, but I get the same issue. I can't use CAAnimationGroup with appropriate beginTimes because I need the animations to loop.
Another thing to note is if I just perform the growing animation with a high repeat count, everything works fine. The only issue is the sequential looping of the two animations. If anyone knows how I can fix this, or knows a different way to sequentially loop two CAAnimations, I will be very grateful.