I believe pinchaser is on the right track.
Here is what happens:
1. the feet get fast
2. the subconscious tries to catch the ball up to the feet by forcing the ball down from the top of the swing.
3. The ball comes screaming down from the top of the back swing and slightly passes the feet.
4. The subconscious feels the ball going past the release point and says "I had better do something quick, if I don't, the ball will not hook, so let me try to flip the ball off my hand by turning my hand over the top of the ball." This makes my elbow get outside of my thumb which causes the chicken wing and kills the roll.
These things can happen by just getting too fast with my feet and can happen at any time.
One thing you can do to fix this problem is Bill Taylor's "belly walk" technique. Just line up in your stance, but place the ball on your belly button and just walk to the foul line without swinging the ball. If you feel weird, then your feet are too fast, you should just be at a normal walking pace when you bowl. Granted some people have a different walking pace than others, but this technique works for all tempos.
Do the belly walk it until it doesn't feel weird, then throw a shot with the same pace, then do the belly walk, then throw a shot, repeat this until you get it down. Do the belly walk before you bowl as a warm up.
The other part to this is to just let your arm swing without forcing it. This will match your swing to your pace as long as you push away on the right step.
Some people have long legs and short arms, short arms and long legs and all different combinations. You will need a video camera or a coach with a good eye to help match your swing up to your feet.
To do it yourself, try to have the ball at your side as your second step (of a four step delivery) compresses.
Ideally the four step sequence should be as follows:
1. push and step
2. ball falls to your side as the second step compresses
3. ball reaches the top of your back swing as the third step compresses
4. The slide the foot should come to a stop as the ball reaches the ankle of your non sliding foot.
If any of the above isn't lining up, adjust your push away so it matches up.