Hmm. If you are looking at this via the embed, there is a slight stutter as the assets are loading which is to be expected. However, when I look at this directly on Codepen, I don't get the stuttering in the animation. I checked on both Chrome and FF.
Aside from that, anytime you want implement animation sequences you should be sure to optimize not only the elements you are animating but they rest of the page as well. Extra calls to the server and large images can slow things down for example so be cognizant of your assets.