Adobe After Effects vertices move sideways when I add more

Hello everyone!

I am a mapper/mapimator who makes videos about battles and wars. But whenever I add vertices to Adobe After Effects it creates them on the opposite side of the shape layer and then moves it over making a weird sideways moving animation. I made a "testing" video just to show what happens. You can see how they move sides, although you can't see the vertices you can very clearly see it moving sideways(in this case up).

Thank you!