N-element pendulum

N-element pendulum, in certain conditions it will break. Why?

Hell if I know, probably some rounding problem from Eulers method, or I messed up matrix math/dimensions or wrongly implemented something, or this Japanese reference I got had something wrong inside, or I missed something.

Update: Source Code included, maybe it will help someone, cause there isn't much in the internet. I also link here awesome japanese paper, that helped me in the way - https://note.com/sciencecafe_mc2/n/ne5077e5a62f1