It seems to me the shape has been animated manually by keyframing two shape layer paths, since it is equal line width throughout. The main thing is that the motion needs to repeat seamlessly. Easiest to make the “main” animation perfectly horizontal. It might be as simple as three keyframes. There is a maximum of two shapes present at a given time, so that’s all you need. In fact, since they are exact duplicates offset in time, the question becomes where and how do you make them match up seamlessly. I think the key to this is having the connecting point between the two shapes traveling at an even speed so that you can match up the pointy end points to it. You could use three evenly spaced and evenly moving nulls as a guideline as to where the end points are and one static null as a reference for where the overall shape starts from.
The bouncy effect may just be a side effect of the animation, not specifically intended. Or you may have to add a keyframe towards the beginning of the animation to widen the shape when it is growing.
If you want that exact look, you could use the video itself as a reference.
Kalleheikki Kannisto
Senior Graphic Designer