This is a pretty good start you have here.
So, one of the things I'm noticing is the legs are changing volume fairly drastically in spots. If you pause on frame one and two and flip between them, you'll see that the thigh switches from being larger that the calf to being smaller. There are spots through the animation that this is happening and I think it might be the main problem.
I made a quick edit trying to take care of the major stuff. I hope this helps.