Euler wrote down the rigid-body equations in 1765, and they already contain the surprise: steady rotation exists about all three principal axes, but only the axes of largest and smallest moment of inertia are stable.
About the intermediate axis, the tiniest misalignment grows exponentially — yet conservation of kinetic energy and of the angular-momentum magnitude bounds the growth, folding it into a periodic end-over-end flip, not chaos.
Cosmonaut Vladimir Dzhanibekov filmed exactly this on a spinning wing-nut aboard Salyut-7 in 1985; physicists had known the theorem for two centuries.
Engineers learned it the hard way when Explorer 1 tumbled in orbit — hence the spacecraft rule: always spin about the major axis.
Something in the simulation stopped unexpectedly — the lesson continues without it. You can move on; nothing you did was wrong.